The Northern Irishman had to battle to make the cut on Friday but played himself into contention with an excellent third round of 64. Even with that effort, however, McDowell started the final day four back of Germany's Marcel Siem.
But Siem's lead quickly disappeared when he found the water twice on the par-3 3rd, en-route to a quadruple bogey seven. Although he played the remaining holes in one-under-par, the German finished a disappointing seventh.
McDowell sprinted to the turn in just 30 shots and rattled off two further birdies on the 10th and 11th. By that stage the 30-year-old Golf Monthly columnist was locked in a ding-dong battle with home favourite Rhys Davies. The Welshman played some scintillating golf to cover the 12 holes between the 4th and 15th in 10-under-par. That incredible streak included two eagle twos - a holed approach to the 439 yard 8th and another at the driveable 15th.
Davies dropped a shot at the difficult 16th but still finished with a course record 62 and posted the clubhouse target at 12-under-par.
"I enjoyed every second. I went out very relaxed,'" said Davies. "I tracked what Graeme was doing. He continued to make birdies, so I kept my head down and tried to make some more."
Although he held a three shot lead, McDowell still had to negotiate the tough closing stretch, played into a headwind. He did so with total control and composure to notch up his fifth European Tour title.
"I think it's the best final round I've ever played to win a tournament," he said. "The first 11 holes was dream golf and I am ecstatic. I feel like I'm in the form of my life right now and I really feel I have a big event in me."
McDowell will go into the US Open at Pebble Beach in two weeks time full of confidence and knowing that good performances in the next two Majors will all but secure his place in Colin Montgomerie's Ryder Cup side for the matches back at Celtic Manor this October.
Another man trying to book his place in that team is Luke Donald. The Englishman completed a highly successful three-week stint on the European Tour, recording a third place finish this week. He ended the tournament one clear of three players who tied for fourth - Robert Rock, Edoardo Molinari and Stephen Gallacher.
The Celtic Manor Wales Open The Celtic Manor Resort, Wales June 3-6, purse, par 71
1 Graeme McDowell (NIR) 72 70 64 63 269 €350,940 2 Rhys Davies (Wal) 67 73 70 62 272 €233,960 3 Luke Donald (Eng) 75 65 69 65 274 €131,813 T4 Robert Rock (Eng) 68 71 70 66 275 €89,569 T4 Edoardo Molinari (Ita) 67 71 70 67 275 €89,569 T4 Stephen Gallacher (Sco) 70 73 63 69 275 €89,569 7 Marcel Siem (Ger) 69 67 66 74 276 €63,169 8 Miguel Angel Jimenez (Esp) 70 68 70 69 277 €52,641 T9 Niclas Fasth (Swe) 69 72 67 71 279 €42,674 T9 Richard McEvoy (Eng) 67 71 69 72 279 €42,674 T9 Thomas Bjorn (Den) 69 68 68 74 279 €42,674
Note: Player score in bold signifies Titleist ball usage only
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Fergus is Golf Monthly's resident expert on the history of the game and has written extensively on that subject. He is a golf obsessive and 1-handicapper. Growing up in the North East of Scotland, golf runs through his veins and his passion for the sport was bolstered during his time at St Andrews university studying history. He went on to earn a post graduate diploma from the London School of Journalism. Fergus has worked for Golf Monthly since 2004 and has written two books on the game; "Great Golf Debates" together with Jezz Ellwood of Golf Monthly and the history section of "The Ultimate Golf Book" together with Neil Tappin , also of Golf Monthly.
Fergus once shanked a ball from just over Granny Clark's Wynd on the 18th of the Old Course that struck the St Andrews Golf Club and rebounded into the Valley of Sin, from where he saved par. Who says there's no golfing god?
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