Stosur, who won the 2011 U.S. Open singles title, and Zhang beat Czech pair Barbora Strycova and Marketa Vondrousova 7-5, 4-6, 7-5 in the last match of the day on Rod Laver Arena. The second-seeded Mladenovic and Babos beat American pair Alison Riske and Jennifer Brady 6-4, 6-2.
The first major in the reunion of Bob and Mike Bryan as a doubles combination ended in a 6-4, 7-6 (3) quarterfinal loss to fifth-seeded Nicolas Mahut and Pierre-Hugues Herbert. The 40-year-old twins reunited in Australia after Bob was sidelined last year with an injured hip. Mike paired with Jack Sock to win the Wimbledon and U.S. Open titles and the ATP Finals.
Mahut and Herbert will meet another American pair in the men's doubles semifinals after Ryan Harrison and Sam Querrey combined for a 3-6, 7-6 (5), 6-4 win over Lukasz Kubot and Horacio Zeballo. Jamie Murray lost twice on the same court in doubles quarterfinals on the same day. He and Bruno Soares went down in straight sets to John Peers and Henri Kontinen in the men's doubles.
In the mixed doubles later on Margaret Court Arena, Murray and Bethanie Mattek-Sands lost 6-2, 7-6 (3) to Australian wildcards Astra Sharma and John-Patrick Smith.
No man has won more Australian Open titles than Novak Djokovic, so obviously he has worked out a routine for getting through the rounds.
After needing less than an hour to get through his quarterfinal match — the six-time champion was leading 6-1, 4-1 when Kei Nishikori retired with a sore right leg — he was asked about the prospect of a final featuring the players ranked No. 1 and No. 2.
"Right now it's my press conference, so it will be nice to talk about me more than Nadal," he said. "If you want to talk about our possible encounter, we talk about that if we both win semis."
Rafael Nadal plays 20-year-old Stefanos Tsitsipas on Thursday in the first of the men's semifinals. Djokovic takes on No. 28-seeded Lucas Pouille on Friday.
Djokovic is back in the semifinals at Melbourne Park for the first time since 2016, when he defended his title to end a sequence of five Australian titles in six years.
He shares the men's record for most Australian titles with Roger Federer and Roy Emerson. After winning Wimbledon and the U.S. Open, the 31-year-old Serb is hoping to make it three major titles in a row.
Djokovic has a 27-25 edge in career-head-to-heads with Nadal, whose 17 major titles include only one in Australia (2009).
Their only career meeting at Melbourne Park was in the 2012 final, when Djokovic won an epic five-setter 5-7, 6-4, 6-2, 6-7 (5), 7-5.
It wasn't the fact he was almost exhausted and playing six-time Australian Open champion Novak Djokovic that caused Kei Nishikori to retire from his quarterfinal match.
"After third game or fourth game when I was serving, I felt pretty heavy to my right leg," he said. "After that I couldn't really bend my knees and couldn't jump up. Yeah, I decided to stop."
Djokovic was leading 6-1, 4-1 when the 2014 U.S. Open finalist retired, making it 15 straight wins to Djokovic in their head-to-head meetings. The eight-seeded Nishikori had had treatment on his upper legs in a medical time out, and a trainer had wrapped the Japanese player's right thigh.
Nishikori said even if it wasn't somebody as formidable as Djokovic across the net, he didn't have enough in the tank to keep going after three five-set matches in his first four rounds.
"I was trying. Like I said, after couple games, I couldn't really move, couldn't hit my serve well," he said. "Yeah, I don't think even if it's Novak, I couldn't beat anybody with my one leg. It was just too tough."
Novak Djokovic advanced to the Australian Open semifinals when Kei Nishikori retired in the second set after less than an hour of play.
Djokovic was leading 6-1, 4-1 when the eighth-seeded Nishikori let the umpire know he couldn't continue. Nishikori, the 2014 U.S. Open runner-up, played three matches that went to five sets in his first four rounds. Two of those went to the new fifth-set super tiebreaker introduced at the Australian Open this year.
Nishikori needed a medical timeout for treatment on his upper leg after the first set. He wasn't comfortable throughout the match, and had his service broken four times.
Djokovic is aiming for a men's record seventh Australian title. He will next play Lucas Pouille, who beat Milos Raonic earlier Wednesday.
Less than two months after hiring Amelie Mauresmo as his coach, Lucas Pouille is into his first Grand Slam semifinal.
It's a rare instance of a woman coaching a man in professional tennis. Mauresmo — who reached No. 1 in the WTA rankings and won two major titles as a player — already had worked with Andy Murray.
"She knows everything about tennis. It's not about being a woman or a man. It doesn't matter," Pouille said when he was asked about Mauresmo during an on-court interview after beating Milos Raonic in four sets at the Australian Open.
"You just have to know what you're doing," Pouille said. "And she does."
Mauresmo, who retired as a player in 2009, was set to be France's Davis Cup captain until she stepped away from that job in December to join Pouille.
Lucas Pouille has reached the Australian Open semifinals for the first time with a 7-6 (4), 6-3, 6-7 (2), 6-4 win over 16th-seeded Milos Raonic, a major reversal of form at Melbourne Park after losing in the first round here in the previous five years.
Pouille entered the quarterfinal 0-3 against Raonic in career meetings — including a first-rounder here in 2016 — but targeted the 2016 Wimbledon finalist's second serve and was only broken once himself in the match.
The No. 28-seeded Pouille had break points in the seventh and ninth games of the third set but Raonic saved and, after an outburst against the chair umpire in the 12th game, dominated the tiebreaker.
The fourth set was on serve until Pouille, who is coached by former Australian Open women's champion Amelie Mauresmo, broke in the last game.
He will next play either six-time Australian titlist Novak Djokovic or eighth-seeded Kei Nishikori.
Milos Raonic has channeled his rage over an umpire's call to force his Australian Open quarterfinal against Lucas Pouille into a fourth set.
Raonic argued over umpire Nico Helwerth's decision to replay a point in the 12th game of the third set, with Pouille on serve.
The 2016 Wimbledon runner-up asked why the ruling was made and, after getting the response, said "because you don't watch, because you're incapable."
Pouille was leading 7-6 (4), 6-3 and held serve to force a tiebreaker, but Raonic won the first six points in the breaker and then finished it off 7-6 (2).
No. 28-seeded Pouille had lost in the first round in his five previous trips to Melbourne Park. This is Raonic's fourth trip to the quarterfinals in Australia.
Tennis great Rod Laver has some advice for the younger generation of Australian players: Get on with business.
Bitter feuding within Australian men's tennis was exposed during the season's first major, when Bernard Tomic and Davis Cup captain Lleyton Hewitt, a two-time major winner and former world No. 1, traded insults.
Nick Kyrgios also took a swipe when Hewitt was watching Alex de Minaur's match while two other Australians were also in action.
"For me, tennis is bigger than that," said Laver, who has the center court at Melbourne Park named in his honor. "There's always a few people in there that are not happy with the world of tennis, but I think you have to compete.
"I think a lot of times it's bad losses that brings up some of the things that come out of your mouth."
Kyrgios and Tomic, both former Wimbledon quarterfinalists, lost in the first round of the Australian Open. Teenagers Alex de Minaur and Alexei Popyrin reached the third round.
The 80-year-old Laver is in Australia for golden anniversary celebrations of his second Grand Slam. He won all four majors in the calendar year in 1962 and '69 and is the only player to have achieved it twice.
His message to the players with unfulfilled talent?
"Some of these other players, I don't know whether they're hanging on or they're unhappy with their own game," he said. "I played, I competed hard, and you shake hands when you lose and you say, 'Hey, but you're not going to get me again.' That attitude is, I think, healthy."
There can be benefits to being on live TV when you're far from home.
Naomi Osaka was on Japanese broadcaster NHK TV after her win over Elina Svitolina in the Australian Open quarterfinals and instead of answering any questions about the match, she asked: "Is this live?" And when told yes, she turned toward the camera and, in Japanese, said: "Grandpa, happy birthday."
She figured her maternal grandfather, Tetsuo Osaka, would be tuning in.
"I was really wanting to win this match because it was his birthday, and I think he would have been watching," the U.S. Open champion explained in a later news conference. "I'm not sure if he's busy right now, but hopefully he got the message."
Osaka is on a 12-match winning streak at Grand Slam tournaments and will next play seventh-seeded Karolina Pliskova in the semifinals.
Karolina Pliskova says her "mind was in the locker room" when she was down 5-1 in the third set of her Australian Open quarterfinal against 23-time major winner Serena Williams.
In one of the most stunning comebacks at the Australian Open, the seventh-seeded Pliskova saved four match points as she rallied to win the last six games to clinch a 6-4, 4-6, 7-5 victory and a semifinal spot against U.S. Open champion Naomi Osaka.
"I didn't have too many chances in the third set. I was a little bit too passive. Obviously mentally down," Pliskova said. "So I just said, 'Let's try this game, on 5-2, maybe I'm going to have couple of chances.'
"She got a bit shaky at the end, so I took my chances, and I won."
Pliskova's win over the seven-time Australian Open titlist means there'll be a first-time women's champion at Melbourne Park this year.
In the other semifinal, two-time Wimbledon winner Petra Kvitova will play Danielle Collins, who had never won a Grand Slam match before this tournament. Kvitova's best previous run at Melbourne was to the semifinals in 2012.
Serena Williams has lost her Australian Open quarterfinal to Karolina Pliskova after being called for a foot-fault on match point.
Williams was serving for the match at 5-1 in the third when the foot-fault was called, and then appeared to roll her left ankle during the next point as she lost three straight points and was broken.
Pliskova saved four match points and won six straight games to advance 6-4, 4-6, 7-5 to a semifinal against Naomi Osaka.
Karolina Pliskova has taken the first set off Serena Williams in their Australian Open quarterfinal.
The seventh-seeded Pliskova broke Williams' serve in the third game and held serve from there to win the first set 6-4, closing with an ace.
The 26-year-old Czech player is one set from becoming just the fifth active player to beat Williams twice or more at major tournaments.
Williams is aiming for a record-tying 24th major title. She lost to Pliskova in the U.S. Open semifinals in 2016, but leads their career head-to-heads 2-1 after winning their quarterfinal match at last year's U.S. Open.
The winner of Wednesday's match will meet U.S. Open champion and fourth-seeded Naomi Osaka in the semifinals.
Naomi Osaka has reached her first semifinal at the Australian Open with a 6-4, 6-1 victory over Elina Svitolina.Osaka used her aggressive style and big hitting to compile a 31-11 edge in winners, including eight aces.
The No. 4-seeded Osaka is the reigning U.S. Open champion. She never had been past the fourth round at Melbourne Park.
Svitolina had her neck and shoulders massaged by a trainer during a medical timeout while trailing 3-0 in the second set.
Osaka's semifinal opponent will be 23-time major champion Serena Williams or No. 7 seed Karolina Pliskova.
Osaka beat Williams for the championship at Flushing Meadows last year in a match filled with all sorts of drama involving the American star and the chair umpire.
Serena Williams and Naomi Osaka can set up a rematch of their chaotic U.S. Open final by winning quarterfinal matches at the Australian Open.
The No. 4-seeded Osaka faces No. 6 Elina Svitolina in the first quarterfinal in Rod Laver Arena on Wednesday.
That will be followed by Williams' matchup against No. 7 Karolina Pliskova.
Osaka beat Williams for the championship in New York last September in a match filled with all sorts of drama involving the American star and the chair umpire.
In Wednesday's men's quarterfinals at Melbourne Park, 2016 Wimbledon runner-up Milos Raonic faces No. 28 Lucas Pouille during the day, while 14-time major champion Novak Djokovic takes on 2014 U.S. Open finalist Kei Nishikori at night.
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