Five-time major winner Phil Mickelson defeated Justin Thomas in a play-off after an extraordinary climax to the WGC-Mexico Championship to claim his first victory since the 2013 Open.

Mickelson parred the first extra hole to become, at the age of 47, the oldest winner of a World Golf Championship event and secure the 43rd title of his career.

Thomas failed to get up and down from the back of the 17th green, the same hole he had three-putted in regulation to kick-start a remarkable sequence of events.

The US PGA champion, who won the Honda Classic in a play-off eight days earlier, then holed his approach to the 72nd hole for an eagle two to set a clubhouse target of 16 under par which looked difficult to catch.

But England's Tyrrell Hatton also reached 16 under thanks to birdies on the 12th and 14th and an eagle of his own on the 15th, while playing partner Mickelson birdied the 15th and 16th to make it a three-way tie.

That tie was broken when Hatton bogeyed the final hole of regulation and meant the 26-year-old had to settle for a share of third with Spain's Rafa Cabrera Bello, who had birdied the same hole in his closing 67.

Mickelson and Thomas headed back to the par-three 17th for sudden death and after Mickelson's birdie attempt had agonisingly grazed the edge of the hole, Thomas missed from 10 feet for par.

Thomas had been 11 shots off the lead at the halfway stage of the €8 million event, but carded a course record of 62 in the third round and a brilliant closing 64, with Mickelson shooting a final round of 66.

"I can't put into words how much this means to me," Mickelson, who had finished fifth, second and sixth in his previous three starts, told Sky Sports.

"It's been a long time and to come through here in Mexico City, with the fans here and to play against the best players in the world and finally come through... I knew it was going to be soon, I was playing too well for it not to be, but you just never know until it happens.

"To be able to share this with my family, my brother (his caddie Tim) and everybody really means a lot, especially knowing all the tough times we've had the last four years."

Asked about the upcoming Masters, a major title he has already won three times, Mickelson added: "My game's starting to get to a level that is some of my best golf and it seems like it's just in time."