Davis Love III posted a 5-under 66 to climb into a tie for second place at 12-under-par 272. He was joined there by Ben Crane (67) and 2004 champion Adam Scott (68). Ryuji Imada posted a 67 to take fifth place at minus-10.
'I had a great week all week. I felt the course has been playing up to my game as the week went on, as it got a bit firmer,' said Garcia, who earned $900,000 for the win. 'I had good a beginning today. I was hitting really, really soft shots.'
The 55-year-old Kite was looking for his first PGA Tour win since the 1993 Los Angeles Open.
Garcia, who won for the sixth time on the PGA Tour, opened with a 14-foot birdie putt on the first. He then dropped his second shot within 4 feet of the cup at the fourth to get to 10 under.
The Spaniard ran home an 18-foot eagle putt at the sixth to move into a tie for the lead. Garcia came right back to birdie No. 7 and move one shot clear of the field.
The 25-year-old birdied the ninth to move two shots clear of Ernie Els. Garcia made it two in a row as he birdied the 10th. After four consecutive pars, he missed the green at the par-5 15th and was unable to save par.
Garcia bounced back with a birdie on the 16th from 22 feet out. Clinging to a two-shot lead heading to the 18th tee, Garcia faced a daunting tee shot with water left of the green.
He missed the green in the right rough. Scott, who could have forced a playoff, found the water directly behind Garcia at 17. Scott bogeyed the hole and that was the cushion Garcia needed. He was unable to get up and down for his par at the last, but the bogey was good enough to give him the win.
With this victory, three of Garcia's six wins have come the week before the U.S. Open.
'I guess I have had the chance of playing great courses the week before the U.S. Open, Westchester twice and also here at the Congressional,' Garcia said. 'It is the tougher courses I feel good playing. I'm definitely looking forward to next week and hopefully I can get it going like this week and give myself a chance.'
Crane, a notoriously slow player, finished second despite some difficulties with his playing partner, Rory Sabbatini, down the stretch. Crane posted four birdies and one bogey on the front nine.
The 29-year-old moved to 12 under with a birdie on 12. Crane struggled to a bogey at the 14th. At that point, the duo was put on the clock due to slow play. Crane parred his next three holes, but Sabbatini wasn't always watching.
On the 17th, Crane was preparing to hit his second shot while Sabbatini was already behind the green waiting to play his fourth after his second shot found water over the green.
Crane knocked his shot on the green. While he was walking up, Sabbatini took his drop and played his fourth. As Crane walked onto the green Sabbatini putted out, then walked to the 18th tee without watching his playing partner finish out. Crane two-putted for par.
Sabbatini closed with a two-putt par at the last after Crane ran in a 30-foot birdie putt to share second.
'As most everyone knows, Rory is a fast player and I am a slow player,' said Crane of the situation. 'The only reason we were on the clock was because of me. Is Rory out of line? No, not really because I'm the one that got us on the clock. It's really an unfortunate situation and I understand how he feels. I do feel bad we got put on the clock.'
Love moved to 9 under with three birdies and a bogey on the front nine. He played the back nine in 3 under to share second place.
Scott, who taught Garcia a new practice drill for his putting earlier in the week, moved to 13 under thanks to four birdies over his opening 15 holes. However, at the 17th, Scott's approach shot bounced off the green, through a bunker and into the water behind the green. That led to a bogey and his sharing second.
Sabbatini finished alone in sixth place at 9-under-par 275. Stuart Appleby, Joe Durant, Els, Matt Gogel, Joey Snyder III and Rod Pampling were one stroke further back at minus-8.
Vijay Singh closed with a even-par 71. He ended in a tie for 29th at 5-under-par 279 and will lose his No. 1 ranking in the world to Tiger Woods heading into the season's second major, the U.S. Open at Pinehurst.