American Brian Harman set an impressive pace in the second round of the 151st Open after tournament officials took the unorthodox step of changing the way the bunkers were raked between rounds.

Masters champion Jon Rahm described Royal Liverpool’s 82 bunkers as “proper penalty structures” after having to play backwards out of one during his opening 74, while Rory McIlroy needed two attempts to escape sand on the 18th in his 71.

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.”

Harman initially had no problems with the bunkers as he made four birdies in succession to surge into the lead, the left-hander holing from 20 feet on the second and similar distances on the third and fourth before hitting the pin with his chip to the par-five fifth to set up a simple tap-in.

Even when he had to play backwards out of a bunker on the 12th and missed the green with his third shot, Harman promptly chipped in for par to remain eight under, four clear of American Max Homa and Scotland’s Michael Stewart.

McIlroy began his second round in ideal fashion with a birdie on the first and, after missing from four feet on the third, got up and down from a bunker on the par-five fifth to improve to two under.

Australia’s Min Woo Lee had set the early clubhouse target on three under following a 68.