Dustin Johnson won his first event since becoming World Number One as the American held off a strong European challenge at the WGC–Mexico Championship.
The US Open champion recorded a closing 68 for a 14 under total at Chapultepec Golf Club.
That was one ahead of England’s Tommy Fleetwood, with Spain’s Jon Rahm and Englishman Ross Fisher sharing third and Belgian Thomas Pieters alongside overnight leader Justin Thomas on 11 under.
Johnson became the fifth player to win their first event since becoming World Number One, following in the footsteps of Ian Woosnam, David Duval, Vijay Singh and Adam Scott as he captured a fourth World Golf Championships title – a tally bettered only by Tiger Woods with 18.
Race to Dubai Rankings leader Fleetwood holed from 40 feet on the last to complete a superb 66 and secure the biggest payday of his career.
Fisher fired nine birdies in a closing 65 and Rahm reeled in Johnson in thrilling fashion before costly bogeys on the 16th and 17th.
Johnson only moved to the top of the Official World Golf Ranking with victory in the US PGA Tour’s Genesis Open a fortnight ago.
"It means a lot because it's a tough spot to be in" Johnson said. "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 Pieters, with Rahm a shot further back.
However, Rahm 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.
Fleetwood's performance will take the 26 year old to a career-high of 35th in the world, 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.
With this win
With the victory, Johnson collects 550 FedExCup points and moves to No. 3 in the standings with 1,353 points, just 384 behind leader Justin Thomas. It took 454 points to qualify for the FedExCup Playoffs in 2016, 633 to qualify for Dell Technologies Championship, 853 for BMW Championship and 1,607 for the TOUR Championship.
Johnson, who won in his last start with a five-stroke victory at the Genesis Open, joins Tiger Woods (18) as the only player with four or more World Golf Championships victories. Johnson’s WGC victories came at the HSBC Champions (2013), the Mexico Championship (2015), the Bridgestone Invitational (2016) and the Mexico Championship (2017).
Johnson earns 1,100 points towards making the 2017 U.S. Presidents Cup team and extends his lead at the top of the list with 7,027 points.
Johnson (2) joins Justin Thomas (3) and Hideki Matsuyama (2) as multiple winners on the PGA TOUR this season.
Johnson becomes the first player to win in consecutive starts on the PGA TOUR since Justin Thomas claimed the SBS Tournament of Champions and the Sony Open in Hawaii in back-to-back weeks earlier this season.
Johnson becomes the fifth player, and first since Adam Scott in 2014, to win his first PGA TOUR start as the No. 1 player in the Official World Golf Ranking.