The world number two held off Ernie Els in a tense finale to the WGC-HSBC Champions to claim the $1.2 million winner's cheque by a stroke after posting 69 for a 17-under-par total of 271.
He also won his battle with rival Tiger Woods, who faded to finish five strokes behind.
Mickelson said that to finish his year by beating the world number one was very satisfying, calling his golf some of the best he has ever played.
"I'm excited about 2010 because I'm starting to play the best golf of my career," said the 37-year-old.
"Everything is starting to come together as far as my driving is concerned. Since working with Butch Harmon my ball-striking has been much better.
"My short game is better than it's ever been and going into 2010, not only am I excited about it, but I have very high expectations."
Mickelson's victory means he is the first person to twice win the tournament - upgraded this year to a World Golf Championship event - 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.
"This was my last event of the year. I won't play again until the end of January in the United States and so to finish the year with a victory was wonderful," he said.
He called wife Amy as soon as he sunk his final putt on Sunday and said she was doing much better.
"She's doing well. She was able to watch at home in the States and she said she was so nervous that she was cleaning out cupboards and stuff, which caught me off guard," he said.
"It's been a fun way to end the year and she is doing much better. We are looking forward to this time off where we can spend some time together, and we have a few family trips lined up."
Beating Woods was a bonus but Mickelson wasn't ready to revel in his victory, aware that his rival has won far more Majors than he has.
Asked if he would talk with him about his winning formula in China, Mickelson relied: "Oh no."
"He has won many Majors and I have not won as many. He has won the US Open and the British Open. I have not. Although it feels great to win the tournament, he has won a lot of events.
"It always feels good to win any tournament, and certainly when you have a chance to go head-to-head with Tiger, although I know he didn't play his best out there."
The American has become hugely popular in China and appears certain to be back next year to defend his title, with other projects in the works.
He is designing his first golf course outside the United States in Tianjin, near Beijing, and plans to open a golf academy in Kunming as part of plans to encourage Chinese children to take up the sport.
"The people here in China have been so nice to me," he said.
"They have been so nice to my family in previous visits and my kids were so disappointed that they were not able to be here this week.
"I hope this win will help the golf courses that I'm designing and the academy because I want to help grow the game."