South Korean-born American James Hahn has upset a host of big names to win a three-man playoff and claim his maiden US PGA title at Riviera Country Club in Los Angeles.

Hahn buried a 24-foot birdie putt on the third sudden-death playoff hole to beat Dustin Johnson after seeing off England’s Paul Casey a hole earlier.

Just weeks away from the birth of his first child, the 33-year-old world No.297 also booked a ticket to the Masters for the first time with the victory.

“This is amazing,” he said.

“I have a little girl coming in three weeks and I never would have thought I would win this golf tournament with so many great players.”

Hahn carded two bogeys in his last seven holes of regulation play for a final-round two-under 69, leaving him at six-under for the tournament.

Johnson, just three tournaments into his return from a self-imposed six-month exile to deal with personal issues, closed with a two-under 69, missing a nine-foot birdie chance on the 18th to win.

He also missed from 12 feet to extend the playoff on the third playoff hole.

Casey bogeyed the last on his way to a 68 in tough conditions.

Japan’s Hideki Matsuyama (67), Australian Open champion Jordan Spieth (70), Spain’s Sergio Garcia (71) and major winner Keegan Bradley (68) shared fourth at five-under.

Garcia, one of seven players who held the lead at some point on Sunday, led by one with two to play only to capitulate to a bogey, bogey finish.

Australian Matt Jones finished with a 68 to tie for 14th at two-under par as he tries to push towards the world top 50 and a return to the Masters.

“This week will be something to draw on in the majors because it was just like one,” Jones said.

“It was playing tough and just mentally draining. Every shot you have to be conscious and aware, you can’t make mistakes anywhere and you can’t miss shots because if you do you get severely penalised. I will bank this and take the experience forward for sure.

Jones, who is projected to move inside the top 80 in the world, says a marked improvement in his putting will be the catalyst to earning a place in the big events.

He is due to play the Arnold Palmer Invitational in three weeks before defending his Houston Open title.

“If I can keep putting the way I am, I am going to have a really good year,” Jones said.

“My ball striking wasn’t at its best this week but my putting was phenomenal. It’s a matter of getting it all together.

“It’s a decent finish this week and something nice to take into a three week break before getting stuck into my next stretch of golf.”

Geoff Ogilvy closed with a 70 to be five-over and tied 49th.