American Brian Harman set a daunting clubhouse target to leave Rory McIlroy with a mountain to climb to end his major drought in the 151st Open Championship at Royal Liverpool.

Harman carded four birdies in a row on the front nine and holed from 15 feet for an eagle on the 18th to complete a flawless second round of 65 and post a 10-under-par halfway total of 132.

That matched the totals recorded at Hoylake by McIlroy in 2014 and Tiger Woods in 2006, although both men were 12 under on their way to lifting the Claret Jug as the course was a par-72 at the time.

Nine years on, McIlroy will head into the weekend nine shots behind Harman after a third birdie of the day on the 18th saw him add a second round of 70 to his opening 71.

Harman, who is bidding to become just the third left-hander to win the Open after Bob Charles (1963) and Phil Mickelson (2013), said: “I’ve had a hot putter the last couple of days so (will) try to ride it through the weekend.

“I’m delighted with how I’m playing. (I’m) just really focused on getting some rest and getting after it tomorrow.

“(I’m) Just not trying to get too caught up in it. It’s just golf. I think when I held the 54-hole lead at the US Open (in 2017) I just probably thought about it too much.”

The 36-year-old’s superb round came after tournament officials took the unorthodox step of changing the way the bunkers were raked between rounds.

Masters champion Jon Rahm described the course’s 82 bunkers as “proper penalty structures” after having to play backwards out of one during his opening 74, while McIlroy needed two shots to escape sand on the 18th.

In response, the R&A instructed greenkeeping staff to build up the edges of the bunkers to allow more balls to roll back into the centre.

“Yesterday afternoon the bunkers dried out more than we have seen in recent weeks and that led to more balls running straight up against the face than we would normally expect,” the R&A said in a statement.

“We have therefore raked all of the bunkers slightly differently to take the sand up one revet on the face of the bunkers.

“We routinely rake bunkers flat at most Open venues but decided this adjustment was appropriate in light of the drier conditions which arose yesterday.

“We will continue to monitor this closely for the remainder of the Championship.”

Even those players who managed to successfully escape from the bunkers on day one had expressed their concerns, with former champion Stewart Cink speaking out following a bogey-free 68.

“Eventually it’ll catch up with you,” the 2009 winner said. “The bottoms of them are so flat that if a ball comes in with any momentum, it’s just going right up to the lip and stop.

“There’s not a little upslope that helps you at all. They are very penal.”