After several minutes were lost when the data system went down, the session got underway with rookie trio Scott McLaughlin, Jimmie Johnson and Romain Grosjean heading out first.
But it was Andretti Autosport’s Alexander Rossi who was first to break into the 60-second bracket with a 60.865s.
Rossi’s team-mate Colton Herta responded by snipping just 0.03s off that lap, with nine-time St Petersburg polesitter Power lowering the barrier by a further 0.02s.
Felix Rosenqvist’s progress was hampered by a technical issue in his Arrow McLaren SP, and when he got underway he outbraked himself at Turn 7.
Newgarden, who has won the last two races at St Petersburg, sprung to the top of the times with a 60.803s with just 11 minutes to go.
“It’s hard to get [tyre] temperature, on the first initial laps,” said the two-time IndyCar champion. “It’s what most are going to struggle with this weekend. But I expect we’ll get more grip the more we run.”
Josef Newgarden, Team Penske Chevrolet
Photo by: Barry Cantrell / Motorsport Images
Sebastien Bourdais caused a brief red when he slithered down the Turn 10 runoff with just under three minutes left, and then stalled as he tried to rejoin.
That left no time for improvements, leaving the top runners incredibly close – with the top 15 covered by just half a second led by Newgarden and Power, with Herta in third closely followed by Andretti team-mate Rossi.
All four Team Penske cars were in the top eight, as Scott Dixon re-established himself as Ganassi’s unofficial team leader in sixth place, with Barber winner Alex Palou in 20th, while Rosenqvist bounced back from his earlier issues to take seventh place and edge team-mate and Barber polesitter Pato O’Ward into ninth – with the Arrow McLaren SP drivers split by McLaughlin.
Fellow rookie Johnson was 2.3s off the pace but only a couple of tenths behind the more experienced Dalton Kellett, although the Foyt driver has not competed in IndyCar at this track before. Grosjean was 19th, 0.8s from the top, but ahead of Barber winner Palou.
Second practice begins at 9.45am local time on Saturday.
IndyCar St Petersburg – FP1 results