Dustin Johnson arrived in Mexico trying to figure out what was wrong with his swing, but left Sunday night with his 20th career PGA Tour victory and sixth World Golf Championship win.
Over 72 holes, only two were worse than par. No one got closer than two shots to him all weekend.
The 34-year-old finished at 21-under 263, the lowest score by five shots in the three years at Chapultepec, closing with a 5-under 66 for a five-shot victory over Rory McIlroy.
"This is a big one for me, and it gives me a lot of confidence for the rest of the year," Johnson said.
The American became the 38th player in PGA Tour history with 20 victories, which makes him a lifetime member when he puts in 15 years.
He won the Saudi International earlier this month and he will return to No.1 in the world next week.
McIlroy did all he could, making six birdies in a seven-hole stretch on the back nine, and closed with a 67.
"I was making birdies and going nowhere," McIlroy said.
"He just played great this week. Hats off to him. He's arguably the best player in the world. And he's got two wins already this year, and he has been one of the best players for a long time."
Johnson finished 10 strokes clear of third-placed Englishmen Paul Casey (65), Ian Poulter (68), and Thailand's Kiradech Aphibarnrat (68).
Australian Cameron Smith made three birdies on his back nine to scratch his way to a one-under-par 70 and a share of sixth place at 10 under, along with Sergio Garcia and Patrick Cantlay, who also both carded rounds of 70.
Tiger Woods got his first top 10 of the year with a final round 69 leaving him 13 shots behind Johnson.
Johnson won the Mexico Championship in 2017 when he was playing the best golf of his life, with three straight victories against the strongest fields, only to suffer a back injury when he slipped down the stairs in his rental house on the eve of the Masters.
"It's the closest I've felt to that since I got hurt two years ago," Johnson said.
"I finally feel like everything is getting very close to where I was then. If I know I'm hitting it well and driving it good, it's going to give me a lot of confidence."