World number one Dustin Johnson held off Spanish rookie Jon Rahm and England's Tommy Fleetwood over Sunday's final holes to win the World Golf Championships Mexico Championship by one stroke.
The reigning US Open champion became only the fifth player to capture his first event after moving atop the world rankings, matching a feat done by Welshman Ian Woosnam, Australia's Adam Scott, Fiji's Vijay Singh and American David Duval.
"It means a lot," Johnson said of the achievement. "It's a tough spot to be in. There's a lot of pressure on you. I came out and hit the ball really well. I played great all week."
After back-to-back 66s, Johnson fired a three-under par 68 Sunday, overcoming two back-nine bogeys with a birdie at the par-5 15th and three closing pars to finish 72 holes on 14-under par 270.
Fleetwood finished second on 271 after closing with a 40-foot birdie putt while Rahm shared third with England's Ross Fisher on 272 with Belgium's Thomas Pieters and American Justin Thomas fifth on 273.
"I played just well enough I guess because I won by one," Johnson said.
It was the second victory in as many starts for the 32-year-old American after taking the title last month at Riviera and marked the 14th PGA triumph of Johnson's career.
Four-time major champion Rory McIlroy, who could have overtaken Johnson atop the rankings with a victory, fired a 71 to share seventh with Americans Phil Mickelson and Brandt Snedeker on 274.
Johnson began a stroke behind Thomas, who opened with a birdie to stretch his edge to two strokes, but the world number one seized command from there.
Thomas never found the fairway at the second and made bogey while Johnson sank a 15-foot birdie putt to share the lead.
Johnson put his approach at the par-5 sixth to five feet and sank the birdie putt to seize the lead alone, then saw Thomas stumble back with a double bogey after finding water at the par-3 seventh and a bogey at eight.
Johnson dropped a 30-foot birdie putt at the eighth and sank an eight-footer at the ninth to make the turn with a four-stroke edge.
But just when Johnson looked to run away, he stumbled with bogeys at the par-4 12th, missing a five-foot par putt, and par-3 13th, finding a bunker off the tee.
That opened the door and late-charging Rahm, a 22-year-old Spaniard in his WGC debut, battered it down.
- Rahm grabbed lead late -
Rahm, who won his first PGA title in January at Torrey Pines with a 60-foot eagle on the final hole, eagled the par-5 11th with a 14-foot birdie and sank a 33-foot birdie putt at 14 to match Johnson for the lead at 13-under par.
Jon Rahm of Spain waves after putting on the second hole during the final round of the World Golf Championships Mexico Championship at Club De Golf Chapultepec on March 5, 2017 in Club De Golf Mexico City Mexico 
Rahm briefly took the lead with a four-foot birdie putt at the par-5 15th, but Johnson, in the final group just behind Rahm, blasted out of a bunker to two feet from the pin and sank a birdie putt at 15 to regain a share of the lead.
The Spaniard missed a six-foot par putt at 16 and an eight-foot par putt at the par-3 17th to leave Johnson ahead by two.
Fleetwood's final birdie capped a round of 66 to keep the pressure on the leader after Rahm faded and Johnson found a fairway bunker off the 18th tee.
But he safely found the green with his approach, rolled his first putt inches from the cup and tapped in for the victory.

Source: AFP