AUGUSTA, Georgia (Reuters) - South Africa's Trevor Immelman, in pursuit of his first major title, preserved his two-shot overnight lead midway through Sunday's final round of the U.S. Masters.

Keeping his composure in difficult, swirling winds at Augusta National, the 28-year-old offset two bogeys with a lone birdie at the fifth to reach the turn in one-over-par 37.

That left Immelman at 10 under overall with most of his rivals struggling on slick greens with tight pin positions and strong gusts of around 50 kph.

Left-hander Steve Flesch was alone in second place after nine holes, with fellow American Brandt Snedeker a further two strokes adrift at six under, also after nine.

Tiger Woods, a four times champion at Augusta and the overwhelming favourite at the start of the week, was struggling to make headway in fourth spot with eight holes to play.

Two ahead of the chasing pack at the start of the final round, Immelman was briefly caught by playing partner Snedeker after the first two holes.

Both players bogeyed the par-four first after failing to reach the green in two before the mop-haired Snedeker rolled in a 40-footer to eagle the par-five second.

Snedeker struck a superb second shot into the heart of the green before sinking a double-breaking putt to get to 10 under.

Immelman, aiming to become the first South African since Gary Player in 1978 to clinch a green jacket, parred the hole after failing to get up and down from the right greenside bunker for birdie.

LOST MOMENTUM

Snedeker then lost momentum, bogeying the third, sixth and seventh

Although Immelman birdied the par-four fifth after hitting a superb approach to four feet, he squandered an opportunity to forge five ahead when he narrowly missed a three-foot birdie putt at the seventh.

The dapper South African dropped another shot at the par-five eighth where he was bunkered off the tee before three-putting from long range, but did well to save par at the ninth with an up-and-down from the left greenside bunker.

Spaniard Miguel Angel Jimenez, who made the halfway cut right on the number, holed out with a seven-iron from the fairway to eagle the par-four seventh on his way to a closing 68.

"It was very satisfying," the pony-tailed Ryder Cup player told reporters after finishing at one-under 287. "It was a tough day there. That eagle helped a lot but the rest of the round was very difficult."

American left-hander Bubba Watson signed off with a 73 and looked forward to watching the rest of the tournament on television.

"Unbelievable, you could see anything," Watson said when asked what the leaders might face over the closing holes.

"Every hole is going to be gusty winds, not sure which direction it's going, not trusting it. I can't wait to watch it."

(Editing by Miles Evans)