Rory Sabbatini carded a second consecutive 67 to take a two-shot lead into the weekend at the WGC Bridgestone Invitational in Akron, Ohio.
The South African had started the day with a one-stroke advantage alongside England's Paul Casey and American Hunter Mahan on three under par.
But while Casey and Mahan mostly struggled in difficult conditions over the Firestone Country Club's testing par-70 South Course layout to record three-over-par rounds of 73, Sabbatini produced a strong finish to surge into the halfway lead.
He was one of only 11 players to shoot under par in hot and humid conditions that peaked at 90 degrees with a breeze that started out light but caused problems in spells throughout the day.
The South African made the turn in 34 thanks to birdies at the first and fifth holes before a bogey at the sixth. Another dropped shot stalled Sabbatini at the 14th but he bounced back with birdies at 15, 16 and 17 before closing with par to leave him at six under for the tournament.
His performance even drew praise from Tiger Woods, whom Sabbatini has in the past claimed to be ‘as beatable as ever’.
‘Great scoring,’ Woods said.
‘Considering the wind was up when he played yesterday and then came up towards probably the middle of his round today.
‘So Rory played beautiful to shoot that.’
Sabbatini revealed it was a patient approach that had paid off.
‘It's a matter of picking and choosing your targets out there,’ he said.
‘There are just opportunities that you have that you can be aggressive but you have to kind of back down and just give the course respect, otherwise it'll hit you pretty quickly.
‘I didn't quite hit the ball as well as I did yesterday. I hit a couple more drives today in that that hay they call rough out there but it was a little more of a grind today, a little more work.
‘I think the positive thing I can take out of it is that I did battle out there today and came out on top.’
Sabbatini will start the third round on Saturday playing alongside Masters champion Zach Johnson, who shot the lowest round of the day with a five-under-par 65 which was later matched by Davis Love III as the former US PGA champion moved to one under.
Woods, Scott Verplank and Kenny Perry are tied for third on two under with five-time event winner Woods carding a 70 after starting his round with a bogey and a birdie before adding another of each on his front nine.
Mahan went out in the afternoon and like Casey shot a 73 to leave him at level par for the tournament.
Open champion Padraig Harrington heads the Irish challenge on one over, seven shots adrift of the leader.
Having taken a week off to celebrate his victory at Carnoustie, Harrington came into the event knowing he would be working hard to rediscover his winning touch in time for the US PGA after a week dominated by media commitments.
And playing an already tough course beefed up with narrow fairways, major-like rough and hard, fast greens, Firestone has proved the perfect place to hone his skills once again.
‘That's what's keeping me going out there this week,’ Harrington admitted following his second-round 69, just one of 11 sub-par rounds on a trying day.
‘I'm not hitting the ball as well as I would want to but I know with the PGA coming around next week I've got to stay in there and work hard.
‘This could be a major championship course, no doubt about that.
‘Certainly the fairways are as narrow as we see, the rough is as heavy. It definitely helps.’
Harrington lies in a tie for 15th place on one over heading into the third round, seven shots adrift of Sabbatini.
Lee Westwood had an inauspicious start to his second round, bogeying his first two holes having teed off at the tenth but steadied himself with a run of six pars before birdies at the 18th, first and third took him to within a shot of Sabbatini.
But dropped shots at the fourth and sixth saw him card a 71 and finish the day one under.
Two bogeys and a birdie saw Colin Montgomerie slip to three over par while Sergio Garcia, playing his first tournament since losing the Open at Carnoustie two weeks ago, posted a round of 77.
The Spaniard started the day at one over and birdied his first hole at the tenth.
However, a bogey at the 16th was followed by a quadruple bogey eight at the 18th before a double bogey at the sixth left him at eight over par.
Canada's Mike Weir withdrew from the tournament citing a neck injury having played ten holes of his second round. His withdrawal reduced the field to 82 players, Jim Furyk having pulled out before the first round began on Thursday with an upper back injury.
