Mickelson triumphed in his 47th attempt at capturing a Major Championship, holing an 18 feet birdie putt at the last to deny South Africa's Ernie Els.
The 33 year old delivered a remarkable parry in the face of a seemingly unbeatable thrust by 2003 Volvo Order of Merit winner Els, charging home in 31 for a third successive 69 and a nine under par total of 279.
In the process Mickelson - another left hander to follow Mike Weir in 2003 - became only the sixth player to birdie the last to win the title by the minimum margin, leaving Els bereft as he saw a fourth Major Championship slip through his fingers as a play-off loomed.
Els, who could already boast two US Open Championships and an Open Golf Championship in his locker, had looked destined to claim the Green Jacket after making two towering eagles at the eighth and 13th holes to soar into the lead.
However it was destined to be Mickelson’s day and Els’s superb 67 was in vain as he finished one stroke shy of a play-off with an eight under par total of 280.
Els, whose next appearance in Europe will be in the 50th Volvo PGA Championship at Wentworth Club next month, was the highest placed European Tour Member during a week in which many featured prominently, including first and second round leader, Justin Rose of England, who finished tied 22nd on 290, two over par.
As well as the popular South African, there were magnificent performances by Spain’s Sergio Garcia, whose closing 66 was the best of the week, and Europe’s Ryder Cup Captain, Bernhard Langer, who tied fourth while England’s Paul Casey shared sixth place on his Augusta debut with 2000 Masters winner, Vijay Singh of Fiji and five others.
Also in the top 20 at the end of a sensational last day were Retief Goosen of South Africa and Ireland’s Padraig Harrington (tied 13th) and Swede Fredrik Jacobson (tied 17th).
After the inclement weather which hindered the spectacle at some recent Masters Tournaments, the 2004 event was packed with a breath-taking array of shot making, eagle putts, holes in one – two in the space of ten minutes with Kirk Triplett following Harrington at the 16th – and coolness under pressure.
Mickelson went into the last day on six under par, tied with fellow American Chris DiMarco and three shots ahead of Els. The South African dropped back to two under par from a starting position of three after seven holes, then caught fire.
Els eagled the eighth from eight feet then repeated the feat at the next par five, the 13th. Suddenly he was seven under par, leading the tournament and three in front of Mickelson, who was playing the 12th.
That is when the 68th Masters ignited in earnest. Mickelson birdied the 12th and 13th then played the shot of the round, almost holing his second at the 14th for a third successive birdie.
Els moved to eight under with a birdie at the 15th, getting down in two from a difficult position, just as he had done in the previous hole for par. Still Mickelson refused to bend under the most intense pressure from a man who had been there and done that before.
As Els made another thrilling par-saving putt on the 16th, then escaped from ‘Sandy Lyle’s bunker’ at the 18th for a solid par, Mickelson holed out for a two at the 16th then came to the last – much like Lyle- needing a birdie to win and a par to face Els in a play-off.
This was Mickelson’s time. His 18 footer caught the left edge of the hole and disappeared, inducing ecstatic scenes around the 18th green. He said: “There is still a feeling of disbelief but it feels awesome. It is an amazing day – the fulfilment of all my dreams. I will remember that unbelievable back nine for ever and ever.
“In the past ten years, to have come so close and fallen short or having people make critical putts against me, makes this difficult journey towards my first Major title so much sweeter.”
Els said: "I did what I had to do. I just kept the faith, kept going. I played as well as I could but I guess Phil deserved this one. He played great down the stretch.
"The noise was unbelievable, probably the loudest I've ever heard it. If you are a fan watching on television it must have been great."
Korea’s KJ Choi finished third on 282, six under par, having made a majestic eagle two at the 490 yard 11th, holing his five iron from the top of the hill. Garcia moved through the field by playing the last 12 holes in eight under par to share fourth with Langer, who carded a level par 72.
The two-time Champion was tied for the lead early in his round but a double bogey at the 15th, where his third shot slid back off the green into the water, halted his momentum. Casey, who played with Langer, had opportunities to finish higher than sixth but had to settle for a 74 and a two under par total of 286.
Langer admitted: “I felt I could pull it off today. I was co-leader early on and I had chances but just didn’t play the back nine well enough.”
However the 46 year old German was impressed with Augusta rookie Casey. He added: “Paul certainly kept his nerve. He enjoyed the atmosphere and just made some silly mistakes. He played much better than he scored. He will store away a lot of good memories that will help him over the next few years.”
The mutual admiration society continued with Casey talking about Langer. The accomplished Englishman commented: “He was fantastic. Very relaxed. He played some fantastic shots and in my opinion I would want him in my Ryder Cup Team if I was the Captain.”
Casey added: “This gives me a real taste for it. It’s been fantastic. The putts didn’t drop but I played some nice golf. I didn’t hit bad shots under pressure. I feel I can win this tournament some day if I keep learning, keep playing away and it could be me standing here with the Green Jacket.”
On a day when the drama never relented, Harrington claimed the fifth hole in one of his career, hitting a six iron into the hole at the 16th from 177 yards on his way to a round of 72 and a level par t4otal of 288. In the next group, American Kirk Triplett proceeded to do the same thing just ten minutes later.
Earlier, Garcia charged home in 31 for a best-of-the-week 66 to set the clubhouse target The Spaniard, who set out nine strokes off the lead, finished on 285, three under par.
Garcia moved through the field with seven birdies and an eagle in his last 12 holes to surpass the 67 by Rose in the first round. Meanwhile Rose trimmed ten shots off his third round effort with a fine closing 71 to repair some of the damage inflicted by his 81 on Saturday.
Rose finished on 290, two under par, having led the field for the first two days and he admitted: “The third round cost me the chance of winning a Major but overall it was a fun week and a good learning experience. Maybe you have to lead a Major a couple of times before you win one.”
Garcia was frustrated by taking a double bogey five at the sixth, but by the time his long birdie putt on the 18th hung on the lip of the cup, he was tied for fifth place as the leaders headed into Amen Corner for the last time.
“Although I shot 66 I felt it could have been a lot lower” said Garcia, who was runner-up to Tiger Woods in the US PGA Championship five years ago.
Two-time past Champion, José Maria Olazábal birdied two of the last three holes for a round of 75 and six over par total of 294. The Spaniard, who had been one behind Rose at halfway, lamented: “The weekend was terrible. Desperate. There is nothing positive I can take from it.”
England’s Ian Poulter closed with a 73 for 295 while 1988 winner, Sandy Lyle of Scotland, shot a 76 for 297. Poulter enthused: “It’s been fantastic to play here for the first time. A huge learning curve. It makes me want to practice even harder to make sure I get back here and that I can contend. I would love to win that Green Jacket one day.”
Meanwhile Lyle, who played all four rounds for the first time since 1999, birdied the final two holes to whet his appetite for 2005. He said: “It’s an achievement every time you play 72 holes here but I didn’t play well over the weekend. That’s been the pattern this season on The European Tour. I’ve made the cut but finished down at the bottom of the class.”