The 34-year-old Swede, putting superbly on the slick greens at Redstone Golf Club, birdied five of his first eight holes on the way to a seven-under-par 65 in the final tune-up event before next week's Masters.
Pettersson, a four-times champion on the US circuit, briefly got to eight under but bogeyed the par-four 17th before finishing level with long-hitting Angel Cabrera of Argentina.
Americans Ricky Barnes and Jeff Maggert were a further stroke back after opening with matching 66s before play was suspended at 2:27 p.m. due to the threat of lightning in the area.
More than an inch of rain saturated the course during the afternoon and organisers later abandoned play for the day with only 51 players having completed the opening round.
Among those who will resume, or start, round one on Friday morning are defending champion Phil Mickelson, three-times major winner Ernie Els and Masters champion Charl Schwartzel.
Pettersson, who reached the turn in five-under 31, was delighted with his score after missing successive cuts at the Transitions Championship and last week's Arnold Palmer Invitational.
"I got off to a great start ... kept it going and got it to eight under," the Swede said after mixing eight birdies with a lone bogey.
"It was a little disappointing bogeying 17, but I gave myself a great chance on 18 and didn't make it. I'm happy with seven under. I played really good ... solid from the tee, hit good irons and putted really well."
Asked what had made the difference following his two missed cuts, Pettersson replied: "I changed my set-up. I opened up my stance and enabled my left hip to really fire through the ball. I play my best when my club really exits left through the ball.
"I felt like I was striking the ball well again, and I told myself this morning just to play aggressive, shoot at the pins and see what happens. Hopefully I can get on a roll here."
Pettersson, who won the most recent of his US PGA Tour titles at the 2010 Canadian Open, made the most of relatively calm conditions at Redstone before the thunderstorm swept across the course later in the day.
"It started blowing on 17 and 18 but other than that, it was perfect," said the Swede, who used a broomstick putter on the greens. "It's always nice to play when it's cloudy. You can read the greens better."
British world number three Lee Westwood and fifth-ranked American Steve Stricker each carded 68s while US Ryder Cup player Hunter Mahan opened with a 69.
Three-times Masters champion Mickelson, who won last year's Houston Open by three shots after closing with a sizzling seven-under-par 65, was one under after three holes when play was suspended for the day.