The 27-year-old native of Argentina tied a competitive course record with a 5-under 65, the best score at the 90th PGA Championship all week, to prove that the course known as "The Monster" could be shaken for a low score.
"I played an excellent round," Romero said through an interpreter. "It was almost perfect."
Play was suspended at 2:16 p.m. ET, shortly before leader J.B. Holmes and the rest of the top scorers were to tee off. Heavy rain, thunder and lightning rocked the course as the players and gallery scattered to find cover.
Romero, in the 12th pairing off the tee, had already put up his score, then hurried out of the weather.
Starting the day at 7 over -- eight shots behind Holmes, seven back of Ben Curtis, Justin Rose and Charlie Wi -- Romero posted seven birdies and two bogeys.
He was even on the day through five holes but closed the front side with birdies on three of the last four holes and added another on No. 10 to get to 3 over. After a bogey on the par-4 15th, he birdied 16 and then finished with two pars.
"Yesterday I was very mad with my round," he said of his 78, which followed an opening 69. "Today, I can't believe it. I can't believe I'm here."
Romero climbed from a tie for 48th into a tie for eighth in the span of four hours.
Others also made a move.
Steve Flesch was 2 under through five holes to get to 1 over for the tournament. Camilo Villegas also had a hot hand, going 4 under through 14 holes to get to 2 over. He was tied there with Boo Weekley, who was 1 under through four holes.
The leaders had been scheduled to tee off in mid-afternoon.
Each day, the leaders had taken advantage of playing in the morning on the long and difficult Donald Ross layout.
Holmes had a 2-under 68 Friday morning when Curtis and Rose posted tournament-low 67s. The first-round co-leaders, Robert Karlsson and Jeev Milkha Singh, both had their 68s after starting their rounds in the morning.
One of the early starters said he didn't think anyone would be going low because the course was getting harder and faster and the wind was gusting.
"If they don't water the greens during the day -- as I think they did on Thursday -- the greens were pretty hard and firm and fast at 9 o'clock so they're going to be really firm and fast by 2:30 or 4 o'clock," said Peter Lonard, who recorded his third consecutive 74 playing in the first twosome of the day. "This is probably the toughest course I've ever played. The rough is high, and even if you're a good driver you're going to miss four fairways. And the greens are tricky; you're always putting up slopes."
Lonard said he thought that a score of 3 or 4 over might win the tournament.
"It's rough," he said. "But somebody's going to enjoy it by the end of the week."
Others near the top of the leaderboard who had yet to tee off in the third round were David Toms (141), Sergio Garcia (142) and Phil Mickelson (143).
Play was suspended for almost 90 minutes of Thursday because of rain, forcing 18 players, including Romero, to finish their first rounds on Friday.