Mickelson hit a shot out of bounds on the 15th hole and hit another shot that struck a spectator in the head, costing him three shots over the last four holes at Quail Hollow in his round of 1-over 73. Watney hit a semi-shank with a 6-iron on the par-3 17th, took double-bogey and had to settle for a 71.
It felt like a small consolation that they were tied at 8-under 208, one shot ahead of George McNeill, who had his share of trouble down the stretch for a 72.
"I can't remember the last time I did that in a tournament, so it was a bit unsettling," Watney said about his shank. "The big picture? I'm tied for the lead, and I would have taken that on Thursday morning."
Instead of pulling away from the pack, their mistakes in a wild final hour allowed a dozen players to get within three shots of the lead.
One of them was Rory McIlroy, who shot 73 and missed seven putts from the 5-foot range or closer, which was no way to celebrate his 24th birthday. McIlroy ranked 82nd out of the 83 players who made the 36-hole cut in the key putting statistic, yet he still goes into the final round with a good chance for his first win of the year.
But it's a crowded race.
John Senden completed his round of 67 some three hours before the leaders finished. Ryan Moore was right behind him with a 68. They were among six players who were tied for fourth, two shots behind. That group included Lee Westwood, who made two birdies and two bogeys in his otherwise boring round of 72.
"It's tough to run away on this golf course," Westwood said. "I think the greens are dictating that with a pretty good bunch. Nobody's going to get streaky and shoot a 62, I don't think. It will be a case of playing solid tomorrow and giving yourself chances and taking opportunities when you can."
The starting time for Sunday has been moved up because of rain in the forecast, with the final round starting at 6:45 a.m. ET. Given the forecast, Mickelson treated Saturday like the final round in case Sunday -- and perhaps even Monday -- is a wash and the tournament is reduced to 54 holes. He made a 7-foot par putt on the 18th to tie Watney.
"It was some poor play coming down the stretch," Mickelson said.
McIlroy didn't need to be reminded that it was his birthday. Fans serenaded or shouted to him on just about every hole. If all he wanted was to make some putts, Boy Wonder didn't get his wish. At times, it became a cruel joke.
He stuffed his shot into just inside 3 feet on the third hole and missed the birdie, and that was just the start of it. He missed another putt inside 3 feet that gave him a double bogey on the ninth hole. Add it up and McIlroy missed seven putts from the 5-foot range, along with a 7-foot putt on the eighth.
After all that, he's still in the mix.
McIlroy, Westwood and more than a dozen have Mickelson and Watney to thank for that.
Right when it looked as though it might be a two-man race, perhaps another duel like they once had at Doral, their blunders opened up Sunday for a slew of others.
Mickelson, 11 under after his 10-foot birdie putt on the 14th hole, pulled his tee shot on the par-5 15th well right of the fairway, just above a cart path. Lefty decided to go for the green by trying to smash his 3-wood with a hard fade around the trees and back toward the green.
Only it didn't fade, and instead went out of bounds.
Mickelson tried it again, this time with his driver, and it turned out the way he wanted, leaving him just short of the green. But he failed to get up-and-down and took double bogey to fall one shot behind. If that wasn't enough, he hooked his approach from a slightly downhill lie in the fairway. The ball struck a spectator in the head and bounded down the hill toward where the old 17th tee used to be located It took Mickelson two chips to reach the green, leading to another bogey.
Just like that, he went from one shot ahead to two shots behind -- but not for long.
"After I made that putt on 14, I felt really good," Mickelson said. "I thought I could get one on 15. I got lucky on the tee shot that didn't go out of bounds. I missed it so bad, but the second shot should not have been a problem."
In the group ahead of him, Watney faced about a 20-minute wait on the tee at the par-3 17th. When it was his turn to hit, Watney hit a semi-shank toward a hospitality tent that left nearly 80 yards short on the 207-yard hole. His next shot barely reached the green, and he three-putted for a double-bogey.
Asked if he was more embarrassed or angry, Watney said, "A bit of both."
"It's a tough hole, and I'm sure guys hit shots they thought were good and it just hooked a little and went in the water and made double," he said. "It just so happened that I'm playing really well and it was on TV, so that's where the embarrassment comes from. But the other thing is you like to put as much distance as you can between you and the other guys, so a bit of anger and definitely some embarrassment."
He tugged his cap over his face on the 18th green and shouted, not willing to share exactly what he said.
"If I have any chance of playing well tomorrow, I'm going to need to get past it and come out ready to go or else I'm going to get run over," Watney said. "I'm looking forward to tomorrow."
McNeill was the steady one in the last few groups, which is not to suggest he didn't have his issues. He sliced his tee shot on the 15th into the middle of a large tree, leaving him no choice but to punch out sideways on a par 5 that he couldn't reach in two, anyway. He wound up reaching this green in four shots, missing a par putt from about 10 feet to drop a shot.
McNeill at least wound up in the final group. And he's not quite sure how he got there.
"Phil looked like he was kind of moving ahead of everyone, and then I don't know what he did on 16, but it looked like either 15 or 16 he had kind of a mess-up," McNeill said. "Then Nick, with the shot that he hit on 17, that actually shook me up probably more than it shook him up. ... Honestly, I didn't even know until I was standing on 18 green, and then I looked and I'm like, 'Oh, wow, I'm tied for the lead.' "
Not for long. He made bogey and fell one shot behind, still in the mix, along with so many others.