The 43-year-old Scot, who complained of tiredness after his 36-hole win over holder Michael Campbell on Friday, struggled to a two-over-par 74 against his opponent's 68.

Montgomerie would have been even further adrift but for a birdie at the 18th, an 18-foot putt that yielded a loud roar of approval from the gallery.

Englishman Casey, who won the China Open and the Johnnie Walker Championship at Gleneagles earlier this season, went seven up at the 22nd hole before two bogeys in three holes allowed the 1999 World Match Play winner a glimmer of hope.

Montgomerie's day was summed up at the par-four eighth where, forced to take an awkward stance by the side of a mound, he shanked his second like a Sunday golfer and then found water with his third stroke.

The 29-year-old Casey effectively clinched victory when he drilled a majestic five-iron to six feet at the par-five 12th and sank his eagle putt.

Montgomerie was gracious in defeat.

"Congratulations to Paul," he said. "I didn't get any breaks really but that's like saying there were four goals offside when you have lost 6-0.

"This proves how good our (Ryder Cup) squad is. We have a fantastic squad and I look forward now to next week."

Up for grabs in Sunday's final is the richest first prize in golf, one million pounds.