The Indy 500 winner took a splash of fuel late in the race, allowing Power to go wide open. That was enough to stay in front of Alexander Rossi, who tried to conserve fuel for more than 60 laps and wound up making one less stop to finish second.
Rossi, the winner the last two races at Mid-Ohio and Pocono, wound up nipping into the points lead of Scott Dixon, who finished third. Simon Pagenaud was fourth and Zach Veach was fifth.
Scott Dixon continues to lead at the halfway point of the IndyCar race at Gateway, though an interesting fuel-mileage race is beginning to develop on the 1.25-mile oval.
Most cars have been able to go about 60 laps between stops, or just shy of a quarter of the 248-lap race. Some drivers, such as Alexander Rossi and Takuma Sato, have been getting good mileage and have been able to extend their pit window to 63 or 64 laps.
In essence, they've been able to turn a four-stop race into a three-stop race.
There's been a crash on the opening lap of the IndyCar race at Gateway Motorsports Park for the second straight year after Sebastien Bourdais got into the outside wall coming out of Turn 2.
Scott Dixon had just led the field to green when Bourdais appeared to lose his car.
The race began about an hour after Schmidt Peterson Motorsports announced that Robert Wickens, who was seriously injured in a wreck last week at Pocono, was breathing with medical help. The Canadian driver also was speaking with his family for the first time since his crash.
His team was fielding only James Hinchcliffe's car in Saturday night's race.
Scott Dixon is on the pole for the IndyCar race at Gateway Motorsports Park, where qualifying was washed out and the series standings were used to determine the starting order.
Alexander Rossi has won the past two races to nip into Dixon's lead. Rossi was also fast in the two practice sessions that were squeezed in ahead of Saturday night's race.
It's the first race for IndyCar since Robert Wickens was involved in a terrifying wreck last week at Pocono. Wickens' car touched Ryan Hunter-Reay's, and he went spinning into the catch fence. His car was obliterated and he was left with serious injuries to his spinal cord and extremities.
Wickens has undergone a series of operations and remains in a Pennsylvania hospital.
More AP auto racing: https://apnews.com/tag/apf-AutoRacing and https://twitter.com/AP_Sports