Harrington rallied back at the final role of regulation play to force the play-off and won the title at the second extra hole.

Harrington's birdie putt never left the hole while Romero's much easier putt slipped by on the right side.

The Irishman had forced the play-off through an excellent finish.

At the 18th, it was Romero who played a superlative pitch to within seven feet, while Harrington's drifted at least 25 feet past the flag.

But the Irishman holed his for a birdie to put the pressure on his opponent, who let his much easier putt slide by on the left side.

Earlier, Colin Montgomerie came perilously close to breaking the St Andrews course record after a superlative performance at the Dunhill Links.

The Scot, Europe's hero at last week's Ryder Cup, got to 10 under for his round after ten birdies and no bogeys during the first 17 holes.

That included a fabulous birdie at the 17th, the famous 'road hole'.

But Monty's sole bogey came at the last, as he put his second shot into the notorious 'valley of sin'.

The course record belonged to Paul Lawrie, who recorded a 63 at this very event last year.

Curtis Strange held the record at 62 before the 'Old Course' was lengthened.

Sandy Lyle birdied the 18th to finish on 17 under, tied with Montgomerie and Fuji's Vijay Singh.

Open champion Ernie Els was forced to pull out after his wife went into labour with the couple's second child.