After two of the best days of his career Paul McGinley slumped to his worst score of the year - a seven-over-par 79 - in blustery conditions at Wentworth.
And now he needs to come from five back to lift one of Europe's biggest titles.
Four clear in the BMW PGA Championship after a record-breaking 13-under-par performance in the opening two rounds, the 41-year-old Dubliner saw Ryder Cup team-mate Robert Karlsson sweep past him into pole position.
Karlsson himself managed a superb 70, which in conditions that caused havoc was bettered by only three players all day.
The 38-year-old, third in the last two European Tour events in Italy and Ireland, now stands 11 under par and four clear of Spain's Miguel Angel Jimenez and England's Oliver Wilson in the race for a first prize of nearly £600,000.
McGinley's closing bogey six dropped him into a tie with Argentina's Daniel Vancsik and Indian Jyoti Randhawa.
McGinley's problems started when he pushed a long-iron off the first tee into a bunker and came up short of the green in two.
He then chipped off the back and after electing to use his putter sent it six feet past and missed the return for a double bogey six.
A pulled drive down the 465-yard third led to a bogey and his next mistake came when he went a fraction long at the short fifth and missed his five-foot par attempt.
He did come back with a birdie on the sixth, but three-putted the 11th and even though he birdied the long 12th - the last hole downwind - Karlsson eagled it after two marvellous shots to 10 feet.
The closing stretch was a challenge for everybody and, try as he did, McGinley just could not prevent further bogeys going on his card at the 13th, 14th, 16th and 18th.
Karlsson, meanwhile, had recovered from a three-putt bogey on the first to turn in a level par 35 and although the eagle was followed by bogeys on the 15th and 16th he hit straight back with two birdies, making a 25-footer on the long next and two-putting the 538-yard last.
Of the other three Irish players who made the cut, Peter Lawrie and Damien McGrane are on one-under, while Graeme McDowell is three shots further back on two-over.
