The Spaniard went the whole of last season on LIV without winning, though he did claim the points title. And he had experienced disappointment before in 2017 at Chapultepec Golf Club when it was a World Golf Championship.

There was no doubt this time after he made a birdie on the reachable par-4 second hole, then holed out for eagle on the next. He played bogey-free to close with a seven-under 64 on Sunday (Monday AEST) for a four-round total of 21 under (263).

"If you would have told me last week on Thursday afternoon that I'd be winning by a six-shot margin this week, I would not have believed you because of how bad I played," said Rahm, who tied for 38th in the Masters. "Hell of an effort."

The week had been filled with uncertainty surrounding the Saudi-funded league, with chief executive Scott O'Neil writing a memo to staff to say LIV was assured of funding through the end of the year, amid reports speculating about the tour's financial future.

LIV announced on Sunday it would be returning to Chapultepec next year.

There was a power outage on Tuesday, fuelling more speculation. The streaming went out for two hours during the opening round. And then Bryson DeChambeau withdrew from the final round, citing an injury to his wrist that he did not want to further aggravate.

DeChambeau, who was trying to become the first player to win three straight times on LIV Golf, was 16 shots behind Rahm when he stopped playing.

"I experienced some discomfort in my wrist during yesterday's round and have decided to withdraw from the final round of LIV Golf Mexico City to prevent further injury," DeChambeau said in a social media post. "Not how I wanted this week to go."

He said he would be evaluated and hoped to be at LIV Golf Virginia on May 7-10, a week before the PGA Championship.

Rahm motored along on Sunday, and so did his Legion XIII team, which won for the first time this year.

David Puig shot 66 to finish second, picking up valuable world ranking points and all but assuring he will be in the PGA Championship. 

Marc Leishman was the leading Australian, finishing at 10 under in a tie for 10th place after firing a 69 in the final round.