Phil Mickelson and Nick Watney each stumbled with the lead on Saturday, leaving the US duo tied atop the leaderboard after three rounds at the US PGA Wells Fargo Championship.
Mickelson took a double bogey at the par-5 15th and a bogey at 16 to hand Watney the lead, only to have Watney double bogey the par-3 17th and leave both even on eight-under 208 for 54 holes in the $6.7 million event at Quail Hollow.
"I was grinding it out there even though I didn't have my A game coming down the stretch," said Mickelson, who fired a 73 while Watney settled for a 71.
"I played poorly coming down the stretch and I'm lucky to be tied for the lead."
American George McNeill was third on 209 with England's Lee Westwood and David Lynn, Sweden's Robert Karlsson, Australian John Senden and Americans Ryan Moore and Derek Ernst another stroke off the pace.
World number two Rory McIlroy fired a 73 on his 24th birthday to stand on 211 with Americans D.A. Points, Kevin Streelman, Brian Harman and Jason Kokrak.
"I don't think I was necessarily scraping it around," McIlroy said. "From tee to green it was actually OK, but when I got on the greens it was a problem. I just couldn't hole anything.
"When you miss a few putts on these greens, you sort of lose confidence in your stroke and then it's just sort of hard to commit fully to what you want to do. If I want to hole some putts tomorrow, I need to do a better job of that."
McIlroy's pals bought him a long-lasting portable phone battery while his girlfriend, tennis star Caroline Wosniacki, had some purchases of her own.
"Got me this new bracelet and a couple pairs of shoes, a bag, sent me a birthday cake, actually I got that in my room today, so all good," he said.
"We were supposed to go for dinner and watch the (Floyd Mayweather-Robert Guerrero) fight somewhere, but it might just be dinner and bed."
Watney knows he and Mickelson allowed a host of rivals back within reach on Sunday, when the threat of storms has prompted organizers to play in threesomes off two tees early in the morning to try and complete the round.
"There are a lot of really good players now two or three shots back," said Watney. "Obviously, you would like to have as much distance as possible, but who knows, maybe this will be a good story."
Three-time Masters champion Mickelson found the right rough at the 15th, put his second shot out of bounds, dropped for a penalty stroke and blasted short of the green then needed three strokes to get down from there.
"The second shot should not have been a problem," Mickelson said. "It was a very easy lie to hit the shot I wanted to. I probably pulled the wrong club. I hit it the second time with the driver to get it to cut. I should have done that the first time. That was a big mistake."
Mickelson struck a spectator in the head at the 16th on the way to a bogey but the left-hander finished with two pars to salvage a share of the lead.
"Following it with a bogey and pulling it to the right and I hit that lady, that just wasn't good," Mickelson said. "But I grinded it out."
He had started with a bogey at the third but answered with birdies at the par-5 fifth, par-4 eighth and par-5 10th. He answered a bogey at the 12th with a birdie two holes later before disaster struck.
Watney's late blunder ensured a shootout on the final day.
"I don't know what happened, to be honest," Watney said. "I was kind of fighting my swing all day, just trying to keep it in play. But obviously that was just a terrible result. I haven't done that for a really long time.
"I can't remember really the last time I did that in a tournament, so it was a bit unsettling. But big picture, I'm tied for the lead, and I would have taken that on Thursday morning.
"Probably wouldn't have liked the way that if you told me that was going to happen. Unfortunately, I can't change it now, so I'm looking forward to tomorrow."