That trio returned to the par-5 18th tee at Westchester Country Club for the first playoff hole. All three players two-putted for par at the first extra hole.
On the second extra hole, Garcia and Sabbatini again two-putted for par. Harrington however, three-putted from the fringe for bogey and was knocked out of the playoff.
For the third playoff hole, it was back to No. 18 for the Spaniard and the South African. Garcia found a fairway bunker off the tee, while Sabbatini's tee ball came to rest in the right rough.
After they both played their second shots down the fairway, Garcia dropped his third shot within 7 feet of the cup. Sabbatini knocked his third on the green just outside 20 feet.
Sabbatini ran his birdie putt passed the cup before Garcia drained his birdie putt for this fifth PGA Tour title and second at this event. He also won the Bron Nelson this year in a playoff.
Vijay Singh closed with a 1-under 70 to end in a tie for fourth, his sixth top-5 and ninth top-10 finish of the season. He was joined at 10-under-par 274 by Tom Byrum and second-round leader Fred Couples.
Garcia began the day at 8 under and fell off the pace with back-to-back bogeys from the par-4 second. He fought back around the turn.
'I did start a bit slow both days, although I felt like I was hitting good shots,' said Garcia, who earned $945,000 for the win. 'I felt like the game was there. I felt like if I was patient and I just kept playing my game, I felt like I could make some birdies because I've done well on this course.'
The Spaniard climbed back to even par for his round with consecutive birdies from the seventh. Garcia kept his hot streak going with birdies at the ninth and 10th to cap a run of four straight birdies that got him to 10 under par.
'I was lucky enough to get on a run there, birdieing Nos. 7, 8, 9 and 10, and then unfortunately I three-putted 12, but some of those holes were playing quite tough,' Garcia said. 'I was expecting to make a couple bogeys here and there, but I knew that I could give myself some good chances at birdies.'
Garcia three-putted for his third bogey of the day at the par-4 12th. However, he came right back to birdie the next. He turned it on down the stretch as well. He birdied the 16th and 18th to get into the clubhouse first at 12 under.
'I felt like it's a course that I can see what I want to do off the tee on pretty much every hole,' said Garcia, who also won here in 2001. 'I like the shots to the green, and I've always enjoyed those tournaments where you don't feel like you're going to birdie every hole. So I think that's probably one of the reasons why I've been fortunate enough to do well here.'
Harrington birdied the third to get to 10 under. He then wrapped bogeys at the fourth and sixth around an eagle on No. 5. The Irishman birdied the seventh and 10th to get to 12 under. On his way to the clubhouse, he dropped a shot at the 13th, but closed with a solid birdie at the 18th to join the playoff.
'Obviously it is a disappointing end,' said Harrington, whose only win in the United States came at the 2002 Target World Challenge, an unofficial event. 'After I got into the playoff I had a good chance on 18 to win the playoff. I hit a good putt, had a very good chance running down to the hole, it just straightened out a little bit at the hole and just missed on the high side. It was a pity. Then on the 17th hole, I probably got a little bit overconfident with my birdie chance. I got a bit aggressive and knocked it 8 feet by.'
Sabbatini, playing in the final group, started at 11 under par and spread two bogeys and two birdies over his opening nine holes. He then birdied the 11th, but faltered to a double bogey at the 12th. He birdied the 15th and 18th to join Harrington and Garcia at minus-12.
'Obviously I was paying attention to the leaderboards,' said Sabbatini. 'I saw that at one point I was two behind and I really decided to pick up the pace again. It's not exactly a golf course where you can go out there and say 'I'm going to birdie this hole, it's an easy hole', because any hole out there can bite you. It really just came down to knowing that people are going to make mistakes and trying to limit mine.'
Luke Donald finished in seventh at 9-under-par 275, while Fredrik Jacobson ended one stroke further back at minus-8.
Cameron Beckman, Tim Clark, Kenny Perry, Chris DiMarco and Bo Van Pelt shared ninth place at 7-under-par 277. Third-round leader Loren Roberts struggled to a 7-over 78 and finished in a tie for 16th at minus-5.