The win for Couch was his first on the PGA TOUR and comes one day before his 33rd birthday.
'Somebody asked me earlier in the week what would be a good birthday present to get me, and I thought if I could win this tournament, that would be the best birthday present,' said Couch, who earned $1,080,000 for the win. 'I just saw that first-place check, it hasn't sunk in yet, but it is absolutely amazing.'
Fred Funk nearly made a miraculous comeback in the final round. He fired a 10- under 62, one off the course record, to end in a tie for second place at 18-under-par 270 at English Turn Golf & Country Club.
Charles Howell III, who played alongside Couch, had a chance to force a playoff, but his 45-foot birdie putt came up short and right of the hole. He shared second with Funk after a closing 65.
Stuart Appleby, a two-time winner this season, notched an 8-under 64 to end in a tie for fourth with Brett Wetterich (66) and Joe Durant (68) at 15-under-par 273.
Couch, who fired a 64 in round three to take the lead, never relented that advantage on the final day despite this being his first PGA TOUR win and having just two top-10 finishes in his tour career.
He flew out of the gates with three straight birdies to open his round, including a chip-in birdie on No. 3 to get to 15 under. Despite that hot start, Couch was only two clear of Howell, who birdied one and two.
Howell got within one as he birdied the fourth. Couch though extended the cushion back to two with an 11-foot birdie putt on the fifth. Howell came right back with a 25-foot birdie putt on six.
Couch sank an 11-footer for birdie at seven and a 7-foot birdie putt on nine to take a three-shot lead on Howell.
Howell cut the deficit to two as he got up and down for birdie at 11. Both birdied the 11th, Howell from 9 feet and Couch from 11 feet. Howell got back to one down with a birdie on 13.
Couch hit his approach stiff at 16 and kick in the 3-footer for birdie and a two-shot lead. At the par-3 17th, he blasted out of a bunker long and into the rough.
The five-time winner on the Nationwide Tour, who chips cross-handed, managed to get up and down for bogey to take a one-stroke lead to the last.
Couch's approach at the 18th flew into a greenside bunker and he was left with a tough lie. He could only advance the ball a few feet into the rough. Couch then chipped in from nearly 55 feet to save par and claim the win.
'I've played a lot better than what I've shown,' said Couch, who had made just two of seven cuts entering this event. 'I've been playing good all year, but my putter has been struggling a little bit and I haven't been scoring well.
'However, my putter came through that last couple of days. I made some really good putts, some clutch putts. That last chip, it couldn't have been a better finish.'
Howell, who was one back and had parred four straight holes, had a birdie try from 45 feet to force a playoff, but could not convert.
'I always had a sneaky feeling that somehow I was going to pull it out today,' Howell admitted. 'I don't know what it was. I got a nice break on my second shot on 15, not going in the water and staying dry.
'The finish was unbelievable. More so than him holing for the par on the last was the bogey he made on 17 from the skulled bunker shot. But it's those things that it takes to win. Chris played great. For a long time there, I was just trying to hang in there with him.'
Funk made things interesting as well. He flew up the leaderboard with five birdies on the front nine that moved him to 13 under.
The 49-year-old birdied five of the first six holes on the back nine to get to 18 under and within one of Couch. However, Funk could not save par at 16 after missing the green left. He got back into a share of second as he ran home at 35-footer for birdie on the last.
Lucas Glover, who played the back nine first in the final round, fired a 9-under 63 to jump to 14-under-par 274. He was joined there by Danny Ellis (65), Tim Herron (67) and Ian Poulter (67).