Denis O’Sullivan and Jimmy Heggarty have a mountain to climb to get back into contention after suffering back-nine collapses on the first day of the Aberdeen Brunei Senior Masters.

Little-known Boonchu Ruangkit of Thailand and Australia’s David Merriman share top spot after they signed for rounds of seven under par 64, but the two Irishmen in the field had to settle for 75s despite both reaching the turn in level par.

O’Sullivan matched one birdie with one bogey on his outward nine, but the two birdies he recorded on his way in could only partially repair the damage caused by three back nine bogeys and a triple-bogey eight at the 12th.

Playing alongside each other, Heggarty could do no better than match O’Sullivan’s total after a disappointing last six holes.

Despite being level par after 12 holes, the Ulsterman, second here last year, could post no better than four over par after a double bogey at the 14th was followed by bogeys on his final two holes.

They weren’t the only ones to struggle though; headline acts Sam Torrance, Sandy Lyle and Ian Woosnam all ended the day over par. Torrance finds himself nine shots off the pace after his round of 73 while Woosnam and Lyle are only one better off at one over par.

Ruangkit and Merriman enjoy a three shot advantage over the field with 36 holes remaining, with four players, including England’s Roger Chapman, leading the chasing pack at four under par.