The Open Champion shot a two over par round today.
Shane Lowry remains in with a chance of claiming his 6th European Tour win and his first of 2020.
He lies four shots adrift of England's Tyrell Hatton (-14) on 10 under par in a share of fourth place after a steady day three at Wentworth.
It began well for the Clara man, a series of pars before a good approach led to a birdie on the 4th, taking him into top spot on the leaderboard.
Coming off the 8th, he found himself two shots clear as his playing partner faltered but Lowry will rue a blip on the par four ninth.
He found the trees from the tee and had to chip out, then left his 8 iron short on approach and three putted for a double-bogey six.
To his credit he followed back up with back to back par's before birdieing the 12th for the third time this week.
Acorn v @ShaneLowryGolf
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However it was obvious that the lapse around the turn had affected him. Bogeys on 16 and 18 coming either side of a thirteenth par on 17, dropping him further away from the final pairing and leaving plenty of food for thought overnight.
Events on the final hole in particular will hurt, a poor drive compounded by a fluffed chip in a torrential downpour left him with a ten footer for par which he was unable to hole.
The Clara man wasn't helped by the form of his playing partner Matthew Fitzpatrick who fell away badly, shooting a four over par round as the field closed up on them.
There is cause for optimism as the course has a history of producing come from behind victories on Sunday.
Lowry did play beautifully for eight holes and that is what he and caddy Bo will have to take from a tough day in tough conditions.
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