The 72 players who made the halfway cut – including Tiger Woods right on the mark of two over par – were also sent out in groups of three rather than two, with defending champion Phil Mickelson alongside past and present US PGA champions Jason Dufner and Keegan Bradley in the first match out.

McIlroy, looking to become just the third man in the modern era after Woods and Jack Nicklaus to win three majors by the age of 25, began his third round just after 11am and immediately saw his four-shot overnight lead cut in half.

The former world number one, who had carded consecutive rounds of 66, found a greenside bunker with his approach to the first and a poor escape led to a bogey five, while playing partner Dustin Johnson holed from three feet for birdie.

With heavy rain having stopped by the time the leaders teed off, Johnson was not the only player taking advantage of the softer greens, fellow American Rickie Fowler picking up four birdies in his first six holes to move to 10 under par before dropping a shot on the seventh.

Former Masters champion Charl Schwartzel had carded a hat-trick of birdies from the fourth before also falling victim to the tough par-four seventh, the South African falling back to eight under.

McIlroy registered his first birdie of the day by two-putting the par-five fifth to get back to 12 under and crucially saved par from 20 feet on the seventh after finding heavy rough off the tee and only being able to hack out onto the fairway.

With Johnson dropping a shot there instead, McIlroy led by three from Fowler - the only player to finish in the top five in both majors this season – with Johnson and Schwartzel a further shot behind.

On the other side of the course, Woods had birdied his first two holes – his only birdie on Friday came on the 18th and ensured he made the cut – and after failing to get up and down from sand on the 15th had also birdied the 16th to lie level par.

McIlroy saved par on the ninth as well after pulling his tee shot left of the green, where it hit a buggy-mounted camera and bounced off the leg of the cameraman.

After making sure the man was unhurt, the buggy was moved and McIlroy pitched to eight feet and rolled in the putt, but Johnson was unable to save par from the other side of the green to drop further off the pace.

Sergio Garcia had moved into a share of second place on nine under courtesy of two superb iron shots which left him birdie putts of just two and four feet on the eighth and ninth.

After finding the cavernous bunker short of the 10th green McIlroy was unable to birdie the par five, but Fowler had picked up a shot there and holed from 30 feet for another birdie on the next.

That took the 25-year-old – whose sole PGA Tour victory came in the Wells Fargo Championship in 2012 – to 11 under par and within one shot of the lead, only for McIlroy to respond with a birdie from seven feet on the 11th.

With no wind and softer greens the scoring was very good, Northern Irish major winners Darren Clarke and Graeme McDowell sharing the clubhouse lead on five under after rounds of 67 and 68 respectively.

Fowler then picked up his seventh birdie of the day, and third in a row, from five feet on the 12th and that was soon good enough for a share of the lead when McIlroy bogeyed the same hole a few minutes later after twice tangling with the heavy rough.