Donald had a one-stroke lead entering the final round of The Heritage and would jump from No. 3 to No. 1 with a victory. Top-ranked Martin Kaymer took the week off.
Westwood, who celebrated his 38th birthday Sunday, opened the final round birdie-bogey and then made eight straight pars.
A birdie on No. 11 was the turning point in Westwood’s round.
“It was probably the hardest putt I had all day — it was 15 feet with 3 feet of break,” he said.
After waiting out a lightning delay on the final hole, he finished off a 3-under 69 for a three-stroke victory over Thailand’s Thongchai Jaidee.
The Englishman totaled 19-under 269 in the Asian Tour event at Royale Jakarta.
As he stepped off the 18th green a portion of the gallery erupted singing “Happy Birthday” — and Westwood had plenty to smile about.
Asked what he wanted for his birthday, Lee replied with a grin, “Something silver and shiny.”
“It was quite a day, really,” he said. “I knew it wasn’t going to be easy with a five-shot lead. I’m experienced enough to know that patience is the key. I hit the ball great, but didn’t hit the putts when it mattered.”
Park Hyun-bin of South Korea briefly shared the lead with Westwood before a bogey on No. 11. Jaidee made a charge but missed a few key putts on his way to shooting a 65.
In Hilton Head Island, South Carolina, Luke Donald remained in position to take the No. 1 ranking, shooting a 1-under 70 on Saturday for a one-stroke lead over defending champion Jim Furyk in The Heritage.
Donald overcame a double bogey and bogey on the front nine to catch Furyk with a birdie on the 16th hole. Donald had an 11-under 202 total. Furyk held the lead for much of the back nine, but bogeyed the closing lighthouse hole for a 69 to drop back. Brendan de Jonge (66) and Scott Verplank (67) were 9 under.
In Chengdu, China, Nicolas Colsaerts set a tournament record at the China Open on Sunday, finishing at 24 under to win by four shots over a group of four players.
The Belgian, who regained his European Tour card only last year, made six birdies in a 6-under 66 to total 264 and beat the old mark by five strokes.
Pablo Martin of Spain (63), Peter Lawrie of Ireland (68), Soren Kjeldsen of Denmark (66) and Danny Lee of New Zealand (65) were next at Luxehills International Country Club in the southwestern city of Chengdu. Prayad Marksaeng in 1996 and Ed Fryatt in 1998 both totaled 19 under to win the tournament.
