The win was the most-lopsided in the history of the 36-hole final match, besting the previous mark of 4 and 3, which was the margin Darren Clarke defeated Tiger Woods by in 2000.
DiMarco trailed 9-down after losing the 26th hole Sunday, but clawed back. He won the 27th, 28th and 30th holes to cut the margin, all the while never quitting despite the almost insurmountable deficit.
'There's drive in me,' said DiMarco. 'They got a good champion. David Toms is solid. He played very well today. My hat's off to him.'
Toms collected his first win of 2005, keeping up the streak of victories by top players on the PGA Tour. All seven winners on tour this season have been ranked in the top-20 in the world rankings.
This was also Toms' 11th win on the PGA Tour and his first since last year's FedEx St. Jude Classic. Toms gets his first WGC title and his second European Tour victory to go along with his 2001 PGA Championship.
Toms, who lost to Woods in the final in 2003, essentially put the tournament away after the opening 18 holes. He and DiMarco were even through nine holes, but Toms captured seven of the next eight holes. The only one Toms did not win was No. 12, which the pair halved.
During that span, Toms tallied five birdies and benefited from some sloppy play by DiMarco. DiMarco bogeyed 16 and 17 to give Toms a 7-up advantage, but DiMarco birdied the 18th to cut Toms' lead to 6-up before the final 18.
The duo halved the first five holes of the second 18 with pars before Toms took control. He rolled in a 4-foot birdie putt at six and one hole later, drained a 40-footer for birdie to win his second consecutive hole. Toms stood 8-up with 11 to play.
DiMarco made a mess of the 26th hole and lost with a bogey. He was 9-down with 10 to play, but the American Ryder Cup and Presidents Cup player did not go away so quietly.
At the ninth, DiMarco converted a 4-foot par putt to cut the margin. He won two in a row at the 10th when his 25-foot birdie putt fell into the hole and now it was a 7-down deficit.
The pair halved 11 meaning DiMarco was 7-down with seven to play and needed to win every hole coming in. He took care of business at the 12th with a 22-foot birdie putt, but the comeback was over on No. 13.
Both players found the fairway off the tee, and both players hit their second shots close. Toms was first to putt with a 7-foot try and poured it into the heart of the cup to close out his victory.
From Friday's third-round win against Phil Mickelson, Toms played nearly flawlessly. He dispatched higher-ranked opponent, Adam Scott, trounced Ian Poulter in the semifinals, then pummeled DiMarco.
Toms's showed no weaknesses during the tournament. His drives found the fairways, his iron play was amazing and Toms holed almost every putt inside 20 feet.
'I've won a few tournaments along the way, but I've never felt this at ease on the golf course,' admitted Toms. 'I felt really good. I felt like I could hit the shot no matter what it was.
'I have no idea how to explain it.'
DiMarco actually jumped out to the first lead of the match at three, but Toms squared the contest with a 4-foot birdie putt at the fourth. DiMarco once again took the lead with a 7-foot birdie putt at the sixth, but he found problems at the difficult, par-4 ninth.
With the honor, DiMarco's drive was ruined by a ringing cell phone during his backswing. The tee ball landed well left of the fairway and DiMarco was frazzled. He missed the green right with his second, then missed a 10-footer for halve, evening the match again.
That opened a gigantic door for Toms. In Saturday's semifinal against Ian Poulter, this stretch of holes around the turn afforded Toms a huge lead. The same could be said for Sunday's final.
Toms knocked a 9-iron to 6 feet to set up birdie and a win at the 10th, a hole he eagled from the fairway on Saturday. Neither player found the green in two at the par-5 11th, but DiMarco's chip from short of the green came up 8 feet short. Toms pitched to 4 feet and when DiMarco's birdie try failed to fall into the cup, Toms sank his for a 2-up lead.
DiMarco hit a solid approach to the 12 feet at No. 13, but Toms trumped him with a second shot that spun back to 2 feet. DiMarco's birdie try flew by the hole on the right side. Toms tapped in to move 3-up.
DiMarco chipped in for birdie twice on Saturday at the 14th hole. Sunday was a different story, however, as he missed the fairway, then had to lay up short of the putting surface. DiMarco's third went over the green and DiMarco did not have the magic he had on Saturday. Toms, whose approach stopped 7 feet from the hole, never needed to pull the putter out of the bag because DiMarco conceded the hole to fall 4-down.
Toms kept pouring it on his Ryder Cup and Presidents Cup teammate. He hit his second at the stick, but spun the ball back to 9 feet. DiMarco left himself 25 feet for birdie, but missed the putt. Toms' birdie try fell right into the center of the cup for a 5-up margin.
Things got worse for DiMarco. At the par-3 16th, Toms came up short of the green on the fringe, but DiMarco hit his tee ball to 36 feet. DiMarco did not handle the downhill putt well, ramming it 15 feet past the hole. Toms stubbed his chip 4 feet short, but DiMarco did not convert his par putt. Toms did, and the rout was on as the former PGA Champion moved 6-up.
DiMarco collected another bogey at 17 when his drive missed the fairway. Tom's lead, almost insurmountable at this point, was 7-up.
Toms missed a 25-foot birdie putt at the par-5 closing hole. DiMarco read the line on Toms' putt and rolled in the 17-footer for birdie to temporarily stop the fantastic charge by Toms.
But DiMarco knew, barring a major meltdown, Toms had the trophy hoisted.
'The stretch on 9-17 got me. He won eight holes. That's pretty tough in match play,' said DiMarco.