Conway had just returned to the track after hitting one of his crew members during a pit stop, an accident that broke the car's front wing. The wing, which helps drivers with their handling of the car, was not fixed before he pulled out.
Conway spun out right in front of Power, who drove into the side of Conway's car, sending it up into the catch fence. Both drivers were able to climb out of their damaged cars.
Power said he didn't understand why A.J. Foyt's team would send Conway onto the track with a broken wing. He said there was no way to avoid the hit that got Conway's car off the track and sent Power's spinning into the inside wall.
"He just spun in front of me. Nothing I could do," Power said. "Good thing is I'm OK, so is Mike, and we'll just look for the next race."
Both drivers climbed out of the car and neither driver was seriously hurt, though Conway told a crew member his back was stiff.
"It started from the pit lane incident," he said. "I came in a little bit too hard and hit a couple of my guys, which I've never done that before. A big apology to them for that. Somebody could have been hurt. Luckily everyone's OK.
"I think at that moment it damaged the front wing, we didn't see. Going down the front straight, I could see it flew up in the air. ... I slowed down going into one, but it just wasn't enough. It just pinched me down and spun the car around."
Three-time Indy winner Helio Castroneves avoided the crash, though a loose, still-bouncing tire careened off his right front tire.
It didn't appear to do much damage to the car, but shortly after that hit, Castroneves started sliding back in the standings, possibly because of a suspension problem.
Also out of the race were Ryan Hunter-Reay and the Lotus cars driven by Jean Alesi and Simona de Silvestro. Alesi and de Silvestro were black-flagged after just 10 laps for not keeping pace with the race leaders.
Michael Andretti, the owner of Hunter-Reay's car, said something broke in the rear end of the No. 28 car.
"We're just lucky we didn't crash really bad," Hunter-Reay said.
Conway has been here before.
Two years ago, with less than two laps to go in the 500, Conway ran into Hunter-Reay and went airborne into the catch fence -- breaking his lower leg and leaving him with an injured back. He missed the rest of the season and failed to qualify at Indy last year.
Conway said he couldn't compare the two hits but lamented he had been knocked out of the race again in a crash.