Molinari - who claimed his only previous European Tour win at the 2006 Italian Open - carded a final round 67 to retain the one-shot lead he took into the final round at Sheshan International GC.
Westwood produced a superb display throughout the week to illustrate why he has moved to the top of the Official World Golf Rankings.
Richie Ramsay and Luke Donald shared third place on nine under, the former securing his place in the Dubai World Championship presented by DP World as a result.
The top five comprised entirely of European Tour members, with Northern Ireland’s Rory McIlroy firing seven birdies in a closing 67 to finish a shot behind Ramsay and Donald.
Molinari was the first to strike on Sunday morning, with a birdie at the second taking him two clear of Westwood. The leading duo matched each other shot for shot for the remainder of the front nine, picking up birdies at the third, fifth and eighth holes, before Westwood reduced his arrears with a three at the tenth.
Molinari spurned an opportunity to extend his lead at the par five 14th hole when he missed a short putt for a four.
The 15th also passed by without a change to either man’s score, although Westwood was forced to hole a superb 12 footer to salvage his par.
Molinari was to pull clear again at the next - a short par four - after Westwood ran into trouble attempting to drive the green.
The Englishman was left with a treacherous pitch over a greenside bunker and had to settle for a par. Molinari, meanwhile, opted to lay up with his tee shot and the move paid off as a superb wedge set up a simple birdie chance, which he duly converted.
Westwood looked set to slip further back at the par-three 17th, after finding the sand, but he once again showed his mettle with a gutsy par putt to remain two behind.
He then found the green in two at 18 to increase the pressure on Molinari, but was unable to sink his eagle putt.
Tiger Woods carded a 69 for a share of 7th place on 7 under.
Padraig Harrington finished with a round of 73 – after double bogeys on the 5th and 18th – to end the event in share of 16th place on 5 under.
Martin Kaymer of Germany signed for 71 to finish two under for the event.
Graeme McDowell was three under of the day – after a 69 - to finish one under par on Sunday.
Phil Mickelson signed for a 73 to drop to one over par for the tournament.
FRANCESCO MOLINARI
• His second European Tour International Schedule victory in his 172nd European Tour event.
• His first European Tour victory since the 2006 Italian Open – a gap of four years and 185 days.
• Played in 125 European Tour events between victories.
• In that time has been second six times. They were: 2006 Omega European Masters, 2008 Mercedes-Benz Championship, 2009 Hong Kong Open (Nov 08), 2009 Portugal Masters, 2010 Alstom Open de France and 2010 Portugal Masters.
• His first WGC victory of his career, in his fifth WGC appearance.
• This victory beats his previous best WGC performance of a tie for tenth in the 2009 WGC – HSBC Champions.
• The third WGC victory won by a European Tour Member in 2010; They are: Ian Poulter (WGC – Accenture Match Play), Ernie Els (WGC – CA Championship) and Francesco Molinari (WGC – HSBC Champions). Since the WGC events began in 1999 this marks the first time three European Tour Members have won three of these events in the same season.
• Becomes the 17th different winner of a WGC event since they began in 1999. Italy now becomes the ninth different country to win a WGC event.
• Joins Darren Clarke, Ernie Els, Henrik Stenson, Vijay Singh, Geoff Ogilvy and Ian Poulter as European Tour Members to win a WGC event.
• Moves into the top 15 of the Official World Golf Ranking; his highest career position.
OTHER FACTS
• Won the 2006 Italian Open, the only other time he has led going into the final round of a European Tour event.
• Fourth Italian victory of the 2010 European Tour season, following his brother Edoardo Molinari (The Barclays Scottish Open and Johnnie Walker Championship at Gleneagles) and Matteo Manassero (CASTELLÓ MASTERS Costa Azahar). This represents the most Italian wins in a single European Tour season.
• The Molinari brothers now join Seve and Maunel Ballesteros, who in 1983 both won, (Seve – PGA Championship, Irish Open and Trophée Lancôme; Manuel – Timex Open), as the only brothers to win in the same European Tour season.
• Victory marks the first time in European Tour history that three different Italian players have won in the same European Tour season.
• The 15th Italian victory in European Tour history.
• Wins for the second time in China having partnered his brother, Edoardo, in Italy’s first win in the Omega Mission Hills World Cup last year.
• Moves to €2,201,613 in The Race to Dubai; his highest total in a single season and the first time he has passed €2 million in a season.
• Moves through €6 million in European Tour Official Career Earnings.
• Gains his highest European Tour prize of €860,153.
• Gains a three year European Tour exemption.
• Second win as a professional.
