Watch: Justin Thomas Drops Eagle at the 18th at WGC Mexico Championship

Phil Mickelson might have clinched his first PGA tournament in over four years but it was Justin Thomas who stole the show at the WGC-Mexico Championship on Sunday.

The former carded a five-under 66 on the final round for a combined 16-under 268 but needed a playoff to break Thomas's resistance and secure a first win on the PGA Tour since he clinched the Open in 2013.

Thomas shot 62 and 64 in the final two rounds, including an unbelievable hole-out for eagle at the 72^nd hole, which momentarily gave him a two-shot lead. The 24-year-old had come close to pull off a hole out eagle at the Honda Classic last week and went one better on Sunday, producing one of the best shots the PGA Tour has seen in years.

Thomas's performance was even more remarkable considering he had followed his win at the Honda Classic last week with two abysmal opening rounds.

Last year's PGA Championship winner trailed leader Shubnakar Sharma by 11 shots after two rounds, which he admitted were "the worst I've ever felt over the ball in my life".

However, Thomas then blitzed the field on Saturday and birdied six of the first 15 holes on the final round, before a bogey at the par-3 17^th appeared to derail his comeback.

His incredible finish ensured he remained in contention for an unlikely back-to-back wins on the PGA Tour but was ultimately pipped to the post by Mickelson.

"If you would have told me I'd be in a playoff after two rounds, I would have told you you were lying," Thomas, who has won seven PGA Tour titles in his last 32 starts, told NBC.

"I played unbelievable golf these last two days. I'm probably more proud of myself than I ever have been."

Mickelson, meanwhile, was pleased to end his winless run and to add another WGC crown to the two he previously won, the last of which came in 2009 at Trump National Doral.

The 47-year-old was in bullish mood when asked whether he feared his success at the Open in 2013 could be the last of his career.

"I knew that wasn't going to be the last one, and this isn't either," he said as reported by Golf Digest.

"I don't know what to say. It's been a tough go the last four years, not playing my best, but to have the belief that I was going to get there and to finally break through and do it was incredible.

"I believe that more is to come, and I feel like I'm starting to play some of my best golf."

The five-time major winner, who became the oldest winner of WGC title, has been steadily building form ahead of The Masters next month, finishing tied-fifth at the Waste Management Phoenix Open, tied-second at the AT&T Pebble Beach Pro-Am and tied-sixth at the Genesis Open.