UPDATE 1-Golf-Wilson two ahead going into Phoenix Monday finish

* Wilson poised to win fourth PGA Tour title

* Leads by two over Gainey, Dufner and Singh (Adds details, quotes)

SCOTTSDALE, Arizona Feb 6 (Reuters) - American Mark Wilson showed nerves of steel as he sank a 15-foot birdie putt at the par-three 12th to move two strokes clear in the final round of the frost-delayed Phoenix Open on Sunday.

For the first time on a marathon day at TPC Scottsdale, he held the outright lead and the siren sounded one hole later to suspend play in fading light with the weather-hit tournament set for a rare Monday finish.

"I've got a two-shot lead, but that could evaporate quickly with an eagle by someone in front of us on 15," Wilson, 36, told reporters.

"I know if I hit good shots coming in, make two or three birdies, I'm probably going to be holding the trophy. If I'm not, someone has beat me and I can handle that."

Wilson, who won his third PGA Tour title at last month's Sony Open in Hawaii, was at 18 under, two ahead of compatriots Tommy Gainey and Jason Dufner, plus Fijian Vijay Singh.

Nationwide Tour graduate Gainey, playing with Wilson in the final group, bogeyed the 12th after three-putting to slip out of a share of the lead while Dufner had four holes to play.

Former world number one Singh, who opted to play the final hole in the gathering gloom, parred the last for a five-under-par 66 to hold the clubhouse lead at 16-under 268.

Big-hitting American J.B. Holmes, a double winner of the Phoenix Open, closed with a 67 to finish at 15-under, level with compatriot Nick Watney (68).

The final round will resume at 0900 local (1600 GMT) on Monday with Wilson and Gainey each facing birdie putts from around 19 feet at the par-five 13th.

"It's just been a long ride -- four holes the first day, 28 holes the next day, then four holes and now 31 holes," Wilson said of the weather-hit event.

"And we'll do five more tomorrow and see what happens."

UNCONVENTIONAL PLAYER

Gainey, one of the PGA Tour's most unconventional players, began the day with a one-shot lead over Wilson and he preserved that advantage by carding a five-birdie 68 in the third round.

After a brief break, the players set off for the final round and Gainey stayed one ahead of the chasing pack when he and Wilson each birdied the par-three fifth.

However, Wilson drew level by sinking a monster birdie putt from 36 feet at the eighth and he and Gainey parred the ninth to reach the turn in a tie for the lead at 18 under.

Gainey, who had not made a cut in three previous PGA Tour starts this season, had a chance to regain the outright lead after hitting a superb approach to six feet at the par-four 10th but his birdie putt slid past the left edge of the cup.

Despite taking a three-wood for safety at the par-four 11th, Gainey bogeyed the hole after pulling his tee shot into water and ending up in a greenside bunker with his third.

He did well to avoid a double bogey by sinking a seven-footer and remained co-leader with Wilson, who also bogeyed the hole after driving into the right rough and finding a bunker with his approach.

Wilson, a die-hard Green Bay Packers fan who wore the Super Bowl team's green-and-gold colours on Sunday, had been ice-cool throughout the round and he benefited from a two-shot swing with his timely birdie at the 12th.

"The day started off good, but right now I'm not too happy," Gainey, who has an unusual baseball-style swing, said of his bid for a maiden PGA Tour victory. "I'm just a little mad at the way I played those last six holes.

"I've just got to come out tomorrow and get it done, just start making some putts," added the 35-year-old from South Carolina who is nicknamed "Two Gloves" for wearing two golf gloves whenever he plays.

(Writing by Mark Lamport-Stokes in Los Angeles; Editing by Frank Pingue/Greg Stutchbury; To comment on this story email sportsfeedback@thomsonreuters.com)

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