One stroke clear at the start of the day, the 30-year-old American birdied three of the last five holes at Royal Liverpool for a five-under-par 67, sealing his 11th career major.
Although chased hard by DiMarco, Woods was always in control and coasted to his third British Open with a superb display of precision golf in breezy conditions.
Shaping the ball as required and putting beautifully, the world number one became the first player to lift the Claret Jug two years in a row since fellow American Tom Watson at Royal Birkdale in 1983.
Having romped to his second Open title by five strokes at St Andrews 12 months ago, the game's leading player completed a successful defence at Hoylake with a 72-hole total of 18-under 270.
"I don't know where to begin," an emotional Woods told a news conference after sealing victory in only his third event since the death of his father Earl on May 3.
"I'm excited and worn out, just so many different emotions to describe right now because it all came pouring out on 18.
"My father has meant so much to me and the game of golf and I just wish he could have seen it one more time."
Woods, who moved into second place alongside fellow American Walter Hagen in the all-time major standings behind only Jack Nicklaus (18), was delighted with the quality of his play.
BEST BALL-STRIKING
"As far as control, that was probably one of the best ball-striking weeks I've ever had," he said.
"That's shaping the ball, moving my trajectory and different heights and really controlling my spin going into the greens."
DiMarco, edged out by Woods in a playoff for last year's Masters, briefly got to within a shot and closed with a 68 to finish second, with 2002 champion Ernie Els a further three strokes behind in third after a 71.
Sergio Garcia, joint second overnight with DiMarco and Els, tumbled backwards early on after missing short putts to bogey the second and third.
Playing in the final pairing with Woods, the Spaniard never replicated the form of his third-round 65 on his way to a 73 and a tie for fifth with Japan's Hideto Tanihara, who closed with a 71.
American Jim Furyk, winner of the 2003 U.S. Open, secured fourth place at 12 under after three birdies in the last four holes gave him a 71.
Woods put paid to DiMarco's challenge with a run of three birdies in a row from the 14th and then burst into tears in the arms of his caddie Steve Williams after tapping in for par at the last.
"Stevie said out on the fairway: 'This one's for dad' and once I'd finished all these emotions came pouring out of me," he said. "I miss my dad so much."
RELAXED MOOD
Woods was in relaxed mood from the opening hole. He narrowly missed long-range birdie opportunities at the second and third before making his first move at the 528-yard fifth, rolling in an 18-foot eagle putt to forge two strokes clear.
Four rock-solid pars followed as he reached the turn at 15-under for the tournament in breezy conditions.
DiMarco, whose mother Norma died of a suspected heart attack nearly three weeks ago, mounted the biggest challenge.
He closed to within a stroke after sinking a 25-foot birdie putt at the short 13th before Woods almost effortlessly stretched ahead, sinking a five-footer to birdie the 14th.
Woods then struck his tee shot at the par-three 15th to within 10 feet of the flag and also birdied the par-five fifth to put the title beyond doubt.
Despite having to settle for his third runner-up finish in a major, DiMarco was delighted to all but secure his Ryder Cup place for September.
"It's awesome to be playing well and performing well when everything is on the line," he said. "I had a lot on the line today and I feel like I've got over my injury and over the hump."
DiMarco has struggled with his game since injuring his back in a skiing accident in March.
Norwegian teenager Marius Thorp won the silver medal as top amateur, holing a 25-footer to birdie the last for a 71 and a share of 48th place at even-par 288.
