Dustin Johnson underlined his status as world number one by holding off the challenge of a strong European contingent to win the £7.9million WGC-Mexico Championship.
Johnson carded a closing 68 at Chapultepec Golf Club to finish 14 under par and a shot ahead of England's Tommy Fleetwood, who holed from 40 feet on the last to complete a superb 66 and secure the biggest payday of his career.
While Johnson collected the first prize of £1.35million, outright second was worth £850,000 to Fleetwood, more than double the £362,000 he won for victory in the Abu Dhabi Championship in January.
Ross Fisher and Spain's Jon Rahm shared third place on 12 under, with Fisher firing nine birdies in a closing 65 and Rahm reeling in Johnson in thrilling fashion before costly bogeys on the 16th and 17th.
Johnson only moved to the top of the rankings with victory in the Genesis Open a fortnight ago and became the fifth player to win their first event since becoming number one, following in the footsteps of Ian Woosnam, David Duval, Vijay Singh and Adam Scott.
"It means a lot because it's a tough spot to be in" Johnson said in a post-round interview broadcast on Sky Sports. "There's a lot of pressure on you and I came out and I played really well.
"I hit the ball great all week. The greens are tough to putt on and I didn't feel like I putted my best, but I really hit the ball well and played just well enough I guess because I won by one."
The 32-year-old US Open champion looked to be cruising to victory when he covered the front nine in 31 to surge into a four-shot lead over Thomas Pieters, with Rahm a shot further back.
However, Rahm - who took out affiliate membership of the European Tour this week to become eligible for the Ryder Cup - closed the gap with an eagle on the 11th and then saw Johnson drop shots on the 12th and 13th.
Rahm took full advantage by holing from long range for birdie on the 14th and another gain on the 15th briefly took the 22-year-old into the outright lead in pursuit of a remarkable second win in his rookie season.
However, Johnson also birdied the 15th in the group behind and was given some welcome breathing space when Rahm three-putted both the 16th and 17th from long range.
Fleetwood kept up the pressure with an unlikely birdie on the 18th, but Johnson produced a superb approach from an awkward lie in a fairway bunker and safely two-putted for his fourth World Golf Championship title.
Fleetwood's performance will take the 26-year-old from Southport to a career-high of 35th in the world rankings, with Rahm up to 25th.
Rory McIlroy began the final round two shots off the lead but was never able to mount a charge, the world number three finishing joint seventh after carding two bogeys and two birdies in a closing 71.
Lee Westwood, who has played in 56 of the possible 61 individual World Golf Championship events without success, was within a shot of the lead after birdies on the first and fourth.
However, the 43-year-old then carded four double bogeys in the space of six holes from the sixth to tumble down the leaderboard, eventually signing for a 78 to finish in a tie for 28th.
Fleetwood admitted he was just playing his own game before he realised he was in with a chance of victory.
He said: "It's tough to beat the best player in the world, isn't it? It was a great back nine. I think I started pretty well after a couple bad shots. So I felt comfortable on the back nine and made the most of those two par fives and a couple more birdies at the last.
"I wasn't overly worried about where the leaders were. Dustin and Jon kind of came backwards a little bit. I didn't know what Jon was doing, I don't know if he made a couple bogeys or double bogey or something.
"To be honest, I was kind of looking at trying to get third on my own at one stage, and then before you know it I saw the scores on the last green and I thought I might have a chance at winning it.
"But it was a really good putt on the last. It was a big one. It would have been nice to get in a play-off and see how we did, but overall it was a good day."