The Northern Irishman topped a strong 18-man field at Thousand Oaks for his first win since October 2010.
The 33-year-old banked a cheque for £624,000 after a four-under round of 68 took him to 17 under for the week.
Aside from his part in Europe's historic Ryder Cup success, 2012 has not been a halcyon year for McDowell and he admitted the win was a big morale boost.
"This really caps off my season," McDowell said, "We try not to put winning on a pedestal, but this one feels very sweet because it's been a grind all year.
"Certainly I will draw some confidence from this one. The game hasn't given me a huge amount this year."
Meanwhile, Martin Kaymer
grabbed his first title of the year with victory at the Nedbank Golf Challenge in Sun City, South Africa. Scotland's Ryder Cup hero Paul Lawrie, the leader after the second round, finished on 74 to be sixth overall.
Kaymer said: "It was always tight. Charl played great golf but I needed a win in 2012.
"I have played very well in the last few weeks and months, but it just did not happen for me on the golf course, so this is great. It's a great way to round off the year."
ICE HOCKEY: Braehead Clan slipped six points behind fifth-placed Coventry Blaze in the EIHL when they were beaten 5-1 in the Midlands last night.
Clan were level at 1-1 when Jade Galbraith netted after 24 minutes to equalise Gerome Giudice's opener.
However, two goals from Russell Cowley and a double from Greg Leeb settled the issue.
BASKETBALL: Glasgow Rocks were beaten 85-73 at home against Leicester Riders in a BBL Championship game last night.