"I had a bit of a dip," Osaka said. "It was really hard for me, I think, emotionally in the second set, because I just started thinking about winning, not exactly the things I could do in order to win."
The tournament moved this year from Key Biscayne to the Miami Dolphins' stadium complex, and Osaka took part in the ribbon-cutting ceremony Wednesday. She found the mix of sun and shadows in the cavernous stadium a challenge.
"It's a little bit tricky to get used to it," she said. "I think for me it got better as time went on. I found comfort in knowing she also was in the same conditions. It's not something that I should really be complaining about."
Defending men's champion John Isner hit 20 aces, lost only 11 points on his serve and beat qualifier Lorenzo Sonego 7-6 (2), 7-6 (7). No. 5-seeded Kei Nishikori was upset by Dusan Lajovic 2-6, 6-2, 6-3. Lajovic improved to 3-14 against top-10 players.
No. 16 Gael Monfils, who has been hampered by an Achilles injury, withdrew before his opening match. In other women's play, Canadian 18-year-old Bianca Andreescu, who overcame a match point to win her opening match, reached the third round by beating No. 32 Sofia Kenin 6-3, 6-3. Andreescu won her first career title last week at Indian Wells.
Three-time champion Venus Williams overcame a wobbly start to beat No. 24 Carla Suarez Navarro 7-6 (4), 6-1.
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