Leishman, who started the final round at TPC Summerlin in Las Vegas tied for 15th, posted nine birdies in a sparkling round of eight-under 63 to get to 19-under par.

He was five shots adrift of runaway winner Sungjae Im, who carded the low round of the day with a 62 to post 24-under 260 - matching the tournament record set by Ryan Moore in 2012 and equalled by Webb Simpson a year later.

American Matthew Wolff (68) was second at 20 under.

Claiming his second PGA Tour title, South Korean Im topped his previous best birdie haul in a PGA Tour round, finishing with nine including four in succession from the 10th to the 13th.

Sungjae Im carded the low round on the final day to claim the title. PHOTO: Getty Images.

Leishman had five birdies on the front nine and four on the back, with a bogey at the 16th his only blemish, as he tied with Rory Sabbatini (64), who now plays under the Slovakian flag, and overnight leader American Adam Schenk (70).

"Well, did everything pretty well, really," Leishman said. "Hit my irons really well. Made the pitches. Yeah, drove it well. So you have to do everything pretty well when you shoot a number like that. To do it on a Sunday makes you feel pretty good.

"It's good just to be playing well, feeling good over the ball, seeing the putts go in. It's been awhile since that's happened and for it to happen at Napa and then here again it's a good feeling. Hopefully I can continue on next week and for the rest of the season."

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Cameron Davis (66) and Matt Jones (70) were the next best Australians in a tie for 27th at 12 under while Adam Scott was in a group a shot further back after a final round 69.

Im, the world No.29, was joint leader after the second round but had dropped to sixth before the start of play on Sunday.

The 23-year-old said he enjoyed the still conditions for a bogey-free round after wind on Saturday made the going tough.

Im was superb from tee to green in the final round. PHOTO: Getty Images.

"The big difference between rounds was no wind and that made it easier," Im told the PGA.

"Tee to green, driver, irons, putting game - it worked as I wanted it to and it gave me a good result."

Im's other PGA Tour victory was at The Honda Classic in Florida in March last year.