'It's been a tough week,' said Goosen. 'The weather has not been all that great, and to pull it off is fantastic.'
Richard Green, who tied for second last week at the Open de France, garnered another runner-up finish along with Lee Westwood and Peter O'Malley at 8-under-par 280.
Goosen showed his front-running ability under pressure two weeks ago to win his second major championship. Back across the pond at The K Club, the South African was as stoic as ever in a bogey-free performance in the final round that pushed him to the top spot in the race for the Order of Merit title.
'I just sort of told myself to slow down a bit,' said Goosen, the leading money winner on the European Tour in 2001 and 2002. 'I got a bit quick yesterday and felt a bit rushed. Today I slowed myself down a bit on the course, which helped.'
Goosen took a one-shot edge over Jose Manuel Lara into the final round and hit his third shot out of a bunker at the par-5 third to four feet for his first birdie of the day. He converted the putt to pull three ahead and drained a 15-foot putt for a birdie at the par-4 fifth to extend his advantage to four strokes.
He had several chances to increase his lead even further on the front nine but calmly walked away with pars to make the turn at 11 under. At the par-5 10th, Goosen reached the green in two after a tremendous drive and two-putted for another birdie on the South Course.
Goosen then parred his next seven holes, en route to completing the back nine without a dropped shot for the fourth straight day. At the par-5 18th, Goosen dropped his third shot inside 5 feet and ran home the birdie putt to cap off his 11th career European Tour title.
'I'm taking a week off,' Goosen said with the British Open looming. 'I'm gonna take it easy next week and go up to Troon and get ready.'
Westwood, who won this event in 1999 and 2000, took himself out of the tournament early on the front nine with a bogey at the fourth and a double bogey at the fifth.
The Englishman responded with back-to-back birdies from the seventh and added a birdie at the 10th to reach 7 under. Westwood added a birdie at the par-3 12th, ultimately coming up short by a wide margin. Westwood had a birdie try at the last to take second place alone but was unable to convert and settled for a 71.
Green tallied three straight birdies starting at the par-5 third before finding trouble with a bogey at the sixth. The Australian birdied two straight from the ninth and picked up back-to-back birdies starting at the 16th to complete his second straight round of 66.
Peter O'Malley collected four birdies and two bogeys for a round of 70.
Lara missed a put at the last that would have put him in the logjam at 8 under. The Spaniard carded a final-round 73 to join Maarten Lafeber in a tie for fifth at seven-under-par 281. David Howell followed at 5-under-par 283.
Angel Cabrera and Soren Kjeldsen shared eighth place at 4-under-par 284.