Mahan's 9-under 62 on Saturday matched the Westchester Country Club record and moved him from a tie for 31st to a tie for third at 12 under -- two strokes behind third-round leader Steve Stricker in the FedEx Cup opener.
The Presidents Cup captain's pick also shot 62s this summer in the Travelers Championship and Canadian Open, both in the first round.
In the Travelers, Mahan followed with rounds 71, 67 and 65 and went on to beat Jay Williamson in a playoff for his first PGA TOUR title. In Canada, the former Oklahoma State star added rounds of 74, 67 and 69 to tie for fifth.
'I feel like it's going to be a little different tomorrow because I have a chance to win the tournament,' Mahan said when asked about the Canadian Open. 'That was a little different and I had three rounds left. Tomorrow, I have a whole different focus of trying to win. So, I'm going to try to put that 62 behind me and just take all the confidence that I gained today and just try to put that into tomorrow and try to win.'
Rich Beem also was 12 under after a 69.
'Must have played some different holes than I did,' Beem said.
Phil Mickelson, seven strokes out of the lead after a 69, planned to attack the course Sunday.
'If I can get off to a good start, I'm going to try to shoot 8, 9, 10 under and see if I can put some pressure on the leaders behind,' Mickelson said.
How aggressive will he be?
'Very aggressive, because I have to shoot an incredible round to catch them,' Mickelson said. 'The front nine will be important. I've got to get some putts to go in. There's a lot of birdie holes on the front nine, and if I can shoot 4, 5, 6 under, I think I can make a good move and have a chance on the back.'
Jim Furyk had some short comments to a small group of reporters after a frustrating round, certainly nothing unusual on the tour. What was unusual was that he made his way to the media tent about an hour later to apologize.
'I just didn't feel like I could leave it like that,' Furyk told the writers, who assured him that they hadn't been offended in any way.
Third in the FedExCup standings, the Canadian Open winner shot an even-par 71 to finish three rounds at 3 under.
J.B. Holmes was 8 under after 13 holes, but dropped strokes with bogeys on Nos. 16 and 17 and parred the par-5 18th for a 6-under 65.
'I had a little rough finish,' said Holmes, eight strokes back at 6 under.
'Just made two bogeys. A couple of bad shots. I was calm all day. Could have been better, but all it comes down to is a great round.'
Holmes drove the par-4 seventh, cutting the corner over the trees on the dogleg left with a 328-yard, 3-wood shot. He then three-putted the three-tiered green for par.
'It could have been better,' Holmes said.
Justin Rose had a hole-in-one on the 139-yard 14th, hitting a 9-iron. 'It hopped just behind the hole and I shouted it in. It's one of the few balls that's ever listened to me,' said Rose, 5 under after a 70. ... At No. 12, leader Steve Stricker is the highest-ranked player in the FedExCup standings without a victory this year. ... Mahan and Steve Flesch (67) had the only bogey-free rounds Saturday. ... Instead of the usual weekend twosomes, threesomes are being used to avoid long delays on the two drivable par 4s. With each group taking a space on the course, 25 threesomes are far more efficient than 37 twosomes and a single.