The 51-year-old former Ryder Cup captain was unable to make any headway in the Seniors Open Championship, instead the Scot succeeded only in losing ground on runaway leader Bernhard Langer at Royal Porthcawl. The German is now expected to claim a second Seniors title having won at Carnoustie in 2010.
He posted a 68 yesterday - his third sub-par round - to move 14 under-par and now goes into the final round a yawning eight strokes clear of Canadian Rick Gibson, with Bob Tway of the United States a further stroke behind.
Having won the US Senior Open and the US Senior PGA Championship, Montgomerie had high hopes of a third triumph. An opening score of 66 on Friday only enhanced his belief that he could win, even if he was seven strokes adrift of Langer. The Scot's ambition persisted when he reached the turn yesterday in a three under-par 32, but then the wheels came off.
Time spent in Porthcawl's punishing rough on the 10th cost Montgomerie two strokes and he became frustrated with himself, bogeying the 11th to go back to four under par where he had started the day. And some nine strokes back from Langer.
He steadied the ship with five consecutive pars but fell into trouble again at the 17th and dropped another stroke and made a mess of the last as well. "Things went terribly wrong on the homeward half," said Montgomerie, who finished with a 72. "I got into all sorts of trouble and the odd bounce landed me in the tough rough."
His compatriot, Andrew Oldcorn, carded a 71 yesterday to move into a share of 36th place - consecutive birdies just before the turn having been followed by eight pars and a solitary birdie.
Former European tour man Ross Drummond was unable to enjoy such consistency as he faltered to a round of 75 - albeit he also shares 36th - with Kenny Hutton a shot further back. Consecutive birdies helped the Scot to an impressive score of 70.