SINGAPORE, Nov 11, 2012 (AFP) - In his first ever play-off, Manassero showed steel beyond his 19 years as he matched the 2010 British Open winner with birdie and par on the first two extra holes and then nervelessly downed the winner at a packed Sentosa Golf Club.
In denying Oosthuizen, Manassero also clinched this season's European money title for world number one Rory McIlroy, making him only the second man to win the merit race on both sides of the Atlantic in the same year.
It settled a marathon final day for the $6 million tournament after storm delays earlier in the week meant Manassero had to play 36 holes in Singapore's tropical heat on Sunday.
"It's been an extremely long day," said Manassero after the $1 million win, the biggest of his career following the 2010 Castello Masters and last year's Malaysian Open.
"The adrenaline kept me going and the key I think was starting really well this morning... and the play-off was a great honour. It's the first play-off of my career, it's been amazing."
Manassero, who in 2010 became the youngest man to make the cut at the Masters and was crowned the European Tour's youngest ever winner, is now also the youngest champion in the Singapore Open's 51-year history.
Oosthuizen has won twice this year but he was forced to revisit the disappointment of the US Masters play-off in April, when he lost out to Bubba Watson's famous hook shot from the trees.
Earlier, McIlroy eagled his last hole for a 65 and third place, three shots behind the leaders. A win for Oosthuizen was the only result which would have delayed him from taking the European money title.
"It has always been one of my goals to become number one in Europe ever since securing my tour card five years ago, but then to also end the year as both European and PGA Tour number one is just amazing," McIlroy said.
Overnight leader Thomas Bjorn finished four adrift on nine-under for the tournament, while three-time winner Adam Scott and Italy's Francesco Molinari shared fifth, one stroke further back.
After lightning storms disrupted the first two days, players were on the course early to complete the third round and Manassero finished with a 64 to take a two-shot lead.
Organisers gambled on fine weather as they pressed ahead with the fourth round, rather than cutting the event to 54 holes, and under fine skies it developed into a duel between the young Italian and Oosthuizen, 30.
Oosthuizen made a great par save after finding water on the seventh hole, and then birdied three in a row around the turn to join Manassero in the lead at 13 under par.
Consecutive bogeys on 12 and 13 seemed to put Oosthuizen out of it -- but he fired back with a chip-in birdie on 14, and when Manassero bunkered on the 15th for bogey, the scores were level again.
A fabulous chip to within two feet on 18 looked to have given Oosthuizen the outright win as he finished his round on 67 for a 13-under-par total of 271.
But under pressure on his last hole, Manassero found two huge shots to reach the green and two-putted from 60 feet to force the play-off with a closing score of 69.
On the first play-off hole, the par-five 18th, Manassero put his second shot into bunkerside rough short of the green while Oosthuizen dropped his 40 feet right of the pin.
Manassero chipped to within three feet, but Oosthuizen pushed his long putt seven feet past the hole before bravely holing out to extend the play-off.
Teeing off again on 18, the South African drove into a fairway bunker but he laid up and then arrowed his approach to four feet, as Manassero again found greenside rough and chipped to 15 feet.
As Manassero missed his putt, Oosthuizen had it in the bag, but his putt lipped out in a scarcely believable miss.
On the third hole, Manassero's second shot rolled off a greenside bank to within 12 feet, and the Italian held his nerve to down the difficult, downhill putt.
"I putted like anyone who would have putted for a win," said Oosthuizen, reliving his miss on the second extra hole. "I was putting beautifully today but the ball just didn't go in. It's been a story for the last four weeks."
Leading final scores at the Barclays Singapore Open on Sunday (par-71):
271 - Matteo Manassero (ITA) 70-68-64-69, Louis Oosthuizen (RSA) 70-69-65-67
Manassero wins on third play-off hole
274 - Rory McIlroy (NIR) 70-70-69-65
275 - Thomas Bjorn (DEN) 66-67-74-68
276 - Francesco Molinari (ITA) 69-67-72-68, Adam Scott (AUS) 71-66-69-70
277 - Anders Hansen (DEN) 69-69-71-68, Chapchai Nirat (THA) 65-73-70-69, Chris Wood (ENG) 70-65-70-72
278 - Jaco Van Zyl (RSA) 68-71-70-69, Y.E. Yang (KOR) 68-73-68-69, Paul Casey (ENG) 68-73-67-70, Adilson Da Silva (BRA) 72-70-66-70
279 - George Coetzee (RSA) 72-63-74-70, Richard Green (AUS) 69-72-69-69, Phil Mickelson (USA) 73-70-69-67
Selected:
284 - Miguel Angel Jimenez (ESP) 74-66-71-73
289 - Colin Montgomerie (SCO) 72-71-71-75