It didn’t take long for the reigning U.S. Open champion to validate his position at the top of the golf world.

In his first start since ascending to No. 1 in the Official World Golf Ranking following his victory in the Genesis Open two weeks ago, Dustin Johnson claimed the World Golf Championships-Mexico Championship by one stroke over Tommy Fleetwood.

Johnson, 32, joined Ian Woosnam, David Duval, Vijay Singh and Adam Scott as the fifth player to win his first start after becoming No. 1.

This one at the Club de Golf Chapultepec in Mexico City didn’t come easy. Johnson began the final round a stroke behind 54-hole leader Justin Thomas before building a four-stroke lead early on the second nine. He briefly relinquished the top spot on the leader board to 2016 U.S. Open low amateur Jon Rahm, but the 22-year-old Rahm bogeyed Nos. 17 and 18 to ultimately end his chances.

Fleetwood birdied the 72nd hole to get within one of the lead, and when Johnson’s tee shot on No. 18 found a tough spot in a fairway bunker, it looked like the duo could be headed for a playoff. But, as he often does, Johnson showed that no situation is too difficult for his talents.

Johnson closed with a 3-under-par 68 for a 72-hole total of 14-under 270. Rahm  finished tied for third with Ross Fisher at 12-under 272. Fleetwood, a member of the 2009 Great Britain and Ireland Walker Cup Team, posted a pair of 66s on the weekend to finish solo second.

“It means a lot,” said Johnson. “Obviously [being No. 1] is a tough spot to be in. There is a lot of pressure on you, and I came out and played really well. I felt like I hit the ball great all week. The greens are tough to putt on. I didn’t feel like I putted my best, and I played just well enough, I guess, because I won by one.”

The win was Johnson’s 14th on the PGA Tour and fourth in a WGC event. He and Tiger Woods, a nine-time USGA champion, are the only two golfers with four or more WGC titles.

Johnson will go for No. 5 in three weeks in the WGC-Dell Technologies Match Play at Austin (Texas) Country Club, which is slated to be his next start.

It also was a good week in Mexico for a couple of other USGA champions.

Brandt Snedeker (2003 U.S. Amateur Public Links), Phil Mickelson (1990 U.S. Amateur) and Rory McIlroy (2011 U.S. Open) shared seventh place at 10-under 274. McIlroy was making his first PGA Tour appearance since injuring his ribs earlier this year. Three-time USGA champion Jordan Spieth tied for 12th, shooting a third-round 63 en route to a 72-hole total of 7-under 277.

Park Place

Given her long absence, some might have wondered if Inbee Park had retired from full-time professional golf. The two-time U.S. Women’s Open champion from the Republic of Korea struggled with a major thumb injury in 2016, limiting her appearances to a handful of events, including a gold-medal performance in golf’s return to the Summer Olympics for the first time in 112 years. “I thought it might take maybe a couple months to get back out on the [LPGA] Tour and get my rhythm back,” said Park.

Two events is all it would take.

After tying for 25th in her season debut in Thailand last week, Park, 28, carded an 8-under-par 64 in Sunday’s final round to win the HSBC Champions in Singapore  by one stroke over 2011 U.S. Girls’ Junior champion Ariya Jutanugarn.

“I thought I was going to be just a little bit rusty,” said Park, who won the 2002 U.S. Girls’ Junior before her Women’s Open victories in 2008 and 2013. “That’s how I felt last week. This week was totally different. Especially the final round was just what I wanted.”

Park started slowly on Sunday before registering nine birdies over a 13-hole stretch starting on No. 5. Even a bogey on the 72nd hole couldn’t derail her quest for an 18th LPGA Tour victory.