American Pat Perez won by two shots in Kuala Lumpur, shooting 24-under, eight shots ahead of Smith.
The 41-year-old only managed to make par on the back nine, but did enough to finish the tournament at 24-under 264 to take home $US1.26 million ($A1.59 million) prize purse and 500,00 FedEX Cup points.
Korea's Sung Kang, a one-time Asian Tour victor, returned with a 65 to take third place while Japan's Hideki Matsuyama, who has two top-five results in the event, and Keegan Bradley of the United States are tied for fourth on 201.
"I did not think I was going to win this week..."
"(I) landed flawless and thought 'Oh made it, it's going to go in, '" Kim said. "I'm still not going to workout".
It was the American's third victory in the PGA Tour after claiming his first title at the 2009 Bob Hope Classic and the OHL Classic in Mexico last November.More news: Goalkeeper dies after freak mid-game collision with teammate
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But Perez responded with three consecutive birdies and signed off with a good four at the long final hole to hit the front on 21 under par, four clear of the in-form Xander Schauffele.
Smith struggled during his second round of 71 and slipped down to joint-third with South Korean Sung Kang (68) and Belgian Thomas Pieters (67).
"Unreal. I think I'm the last guy that expected to win this week, to be honest with you", Perez told reporters after the win.
Bradley, the 2011 PGA Championship victor, recorded his best finish since he was runner-up at the 2014 Arnold Palmer Invitational. "That's all I'm doing", he quipped.
The American will be joined at the Majlis course by defending champion Sergio Garcia, who followed his triumph in Dubai past year by ending his wait for a major at the US Masters. I'm going to work hard and I'm just going to - I'm just taking it a day at a time, I really am.