The 2016 campaign in the US-based open cockpit series begins Sunday over a 1.8-mile (2.89km), 14-turn temporary street circuit with New Zealand's Scott Dixon trying to defend his season points title, won on a tie-breaker of Colombia's Juan Pablo Montoya last August.
Team Penske racer Power's lap on 1min, 0.9431 of a second at 106.329 mph was the best for any of the 22 drivers set the compete for the crown, but still .3 off the track record lap Power set last year in winning his fifth pole position at St. Petersburg.
On only his fifth practice lap, Power crashed entering turn nine. The car sustained heavy right-side damage when it hit the wall.
Power, the 2010 and 2014 winner in St. Petersburg, said he was adjusting the brake when the vehicle hit a bump and he lost control, forcing mechanics to repair it before the second practice session.
"Definitely a bad start," said Power. "But full credit to the guys to get the car back out there, get some laps, get my head around the track and so on. It was a good session. (We) ran in circles with the setup, but P1, pretty happy."
Dixon, a 38-time IndyCar race winner, was second fastest at 1:00.9573 (106.304 mph) for Chip Ganassi Racing. The three-time St. Pete runner-up seeks his first checkered flag on the Florida layout.
"Pretty happy," said Dixon. "St. Pete is a bit of a thorn in our side. I think the car has some good potential. Hopefully we can carry that through. Definitely for us it's always a tricky track. Hopefully we can start near the front and make the most of it and have a strong start to the season."
France's Simon Pagenaud, Power's teammate, was third on 1:01.1796.
Montoya, the defending St. Petersburg race champion, was 10th in the practice session.
"Overall it was a pretty good first day," Montoya said. "I'm pretty happy that we were able to get in a lot of running and we worked on a lot of things. I had too much understeer in the car but we will work on that."
Power won six poles last season and led the most laps in four races but only won once, at the Indianapolis road course race, while Montoya won only twice, at St. Pete and the Indianapolis 500.
Dixon won at Long Beach and Texas and took the season-ender at Sonoma to capture the season crown by having won once more than Montoya over the 16-race campaign.
This year's 16-race calendar will not have races in New Orleans, Milwaukee and Fontana, California, from 2015 but new races were added at Boston in September, an oval in Phoenix in April and at Road America in June.
The feature event will be the 100th running of the Indianapolis 500 on May 29.