Leishman made eight birdies in a seven-under 65 round to set the clubhouse lead at 14-under par.

However, 24-year-old American Champ, the overnight leader, holed a four-foot birdie putt on the last hole to finish at 17 under and win by a shot from Canada's Adam Hadwin.

Champ shot a closing 69 while Hadwin put the most pressure on him with a 67.

Champ was playing with a heavy heart, his thoughts with his grandfather who has advanced stomach cancer.

He said he felt a strange sense of calm as he stood over the putt for victory.

"That putt, it was the first time I didn't really feel that nervous," a tearful Champ said after hugging his father and briefly speaking to his grandfather by phone on the 18th green.

Champ hugs his father while on the phone to his grandfather. PHOTO: Jonathan Ferrey/Getty Images.

"I don't know if it's meant to be or what not, but to win here, no matter whether I win one more tournament, 10 more tournaments, this will be the greatest moment of my golfing career for sure.

"It means everything. Going through this experience has opened my mind up to a lot of things."

Big things have been expected of Champ, who led the PGA Tour in driving distance in his rookie season last year, with an average hit of 326 yards.

He wasted no time notching his first victory 11 months ago but did not contend after that until this week.

Australian journeyman Cameron Percy gave his career a great boost in his latest return to the PGA Tour, finishing tied seventh at 12 under after a closing 67.

First-round co-leader Adam Scott rounded out his week with 68 for a share of 17th, while fellow Australians Aaron Baddeley (71) and Rhein Gibson (73) finished in a tie for 33rd.