Scott shared the overnight lead with former US Open champion Jim Furyk and started his round in perfect style, chipping in from just off the 10th green for a birdie.

That took him into the outright lead on six under but he was soon joined by Westwood, still seeking his first major title at the 63rd attempt after letting a two-shot lead slip going into the final round of the Open at Muirfield last month.

Westwood teed off in light drizzle and made regulation pars at the 10th and 11th before the rain became progressively heavier to threaten another stoppage in play after yesterday’s 70-minute delay.

That did not stop the former world number one from rolling in a 25ft birdie putt on the 12th however, and although he was unable to birdie the par-five 13th for the second day running – he missed from four feet immediately after the stoppage yesterday – he did pick up a shot on the next.

Scott regained top spot when his birdie putt from 15ft on the 13th just had enough pace to trickle into the hole, and he was soon two clear as Westwood dropped his first shot of the week on the 17th.

Seeking to become the first man since Jack Nicklaus in 1975 to win the Masters and US PGA in the same year, Scott then missed a great chance to move three ahead, his birdie putt from six feet on the 15th catching the edge of the hole and spinning out.

In contrast, defending champion Rory McIlroy was facing a battle to make the cut after getting off to a disappointing start to his round.

McIlroy has been watching videos of his eight-shot triumph at Kiawah Island last year for inspiration and it looked to be paying off as he birdied three of his first four holes yesterday and eventually carded a one-under 69.

But the world number three carded two bogeys and a double bogey in his first eight holes today to drop back to two over, right on the early projected cut line.

Meanwhile, Jamie Donaldson had earlier withdrawn from the final major of the year before play began, the Welshman citing a back injury after an opening round of 80. He joined American Bo Van Pelt in making an early exit, Van Pelt citing a hip injury after his own round of 80.

Scott did move three clear when he birdied the 16th, but promptly gave the shot back with a three-putt bogey on the 17th, which was playing the hardest hole of the course.

At seven under he led by two from Furyk, who was still more than two hours away from beginning his round, with Westwood dropping back to four under with a bogey on the uphill second.

Ryder Cup team-mate Martin Kaymer was also four under after covering the back nine in 33 thanks to birdies at the 15th and 16th, but McIlroy’s woes continued with another dropped shot at the first taking him to four over for the tournament.