Runner-up to Australian Geoff Ogilvy last year, Casey triumphed with a par four on the 24th - the longest match of the week - after his Colombian opponent snap-hooked his drive.

Villegas did well to find it in the middle of the desert scrub and, although it was in a bush, he was able to hack it back onto the fairway.

While he hit his third to 30 feet beyond the flag Casey's approach came up short of the green, but he chipped to five feet and after Villegas missed, he holed.

There was a possible difference of almost $900,000 (€662,105) between winning the semi-final and losing it.

If Casey then beat Poulter in the 36-hole final - it began almost immediately - he would earn over $900,000 (€662,105), whereas losing to Villegas would have sent him into an 18-hole third-place play-off against Sergio Garcia. Losing that would leave him with $482,280 (€354,800).

At stake between the two men handed wild cards into the last Ryder Cup by captain Nick Faldo was not just the money, but the world number five spot - and, of course, a treasured victory on American soil.

Casey achieved his maiden win in the States in Houston last April, but Poulter's best finish was second at The Players Championship last May.

Both also knew that lifting this trophy would make them near certainties for this October's Ryder Cup in Wales - without needing to be picked.

As soon as Casey had shaken hands with Villegas, the only player so far to take him past the 14th hole this week, he was taken in a buggy back to the practice putting green.

There he was met by Poulter, dressed all in pink, and they walked together to the first tee.

Villegas was left to rue a missed putt of under three feet in the fast-fading light yesterday evening, but had to gather himself again to take on Garcia at lunchtime.