The world number two showed nerves of steel to claim the US$1.2 million winner's cheque by a stroke from the South African after hitting 69 for a 17-under-par total of 271.

USPGA Tour stalwart Ryan Moore came third after his 68 left him on 15 under, while Northern Ireland's Rory McIlroy powered himself up the leaderboard with a 63 to come fourth a stroke further back.

American Nick Watney was fifth on 275.

Woods, who started two behind Mickelson, faded with an error-strewn front nine. He recovered on the way home but a bogey at the last summed up a frustrating day for the world number one.

He ended with a 72 in joint sixth, five off the pace alongside Germany's Martin Kaymer.

Mickelson's victory means he is the first person to win the tournament - upgraded this year to a World Golf Championship event - twice, after his triumph in 2007.

And it was the best possible way to finish a difficult season interrupted by a break to care for his wife and mother, who were both diagnosed with breast cancer.

"It feels terrific. It's my last event of the year and to finish the year like this is just wonderful," he said.

"Everyone had been expecting Tiger and myself to shoot in the mid-60s and pull away but it was the groups ahead of us (...) making the putts.

"Ernie, and Rory McIlroy, played one of the greatest rounds and I was fortunate to come out on top. It feels good because I had to fight very hard."

Els, desperate to win his first tournament this year and keep intact his commendable record of taking a title every year since he turned professional in 1989, had only himself to blame for finishing second.

He went to the 18th with a one-stroke lead but found the water after botching his approach to the green and finished with a bogey, spoiling an otherwise immaculate round of 63, which matched the course record.

But he was happy to finally find some form again.

"Today was a wonderful day. I mean, I had a really good time," he said.

"For me to come back, to actually share the lead, was quite nice. I'm disappointed about the 18th but I'm going to really think about the 63 I shot today."

The left-handed Mickelson is hugely popular in China and massive crowds followed him and Woods, who were paired together, on a hot and humid day.

Mickelson picked up a shot on the third but slipped up with bogeys on the fourth and fifth after fluffing easy putts.

He compensated by gaining a shot on the seventh and with Els running hot in front of him, picked up consecutive birdies on the 13th and 14th to set up a tense finish.

He missed the green on the crucial 16th but sank an under-pressure 18-foot putt to save par and a birdie on the 17th put him back in the lead.

Mickelson held his nerve coming down the last with a par to win only his second World Golf Championship event in his 29th appearance.

In contrast, Woods self-destructed with a double bogey on the fourth, when he drove his ball into an adjacent canal and had to take a drop.

It didn't get any better with another bogey on the sixth and he was clearly frustrated.

When a camera clicked as he was teeing off at the seventh and his shot found a bunker he shouted "I just can't get a swing" and started swearing under his breath.

"Today was anything that could go wrong went wrong for me," he said. "Just one of those days where I didn't put it together at the right time."