Westwood, who won with a 23-under-par total of 265, had broken the course record with a 61 in the third round and said: "I have never shot this low over the last two rounds before."
Despite his brilliance he came to the last hole thinking he needed a birdie three to win the title because Clarke had closed to within one shot after birdies at the 14th, 15th and 16th.
"I thought Darren would birdie the par-five 17th as well and as I didn't know what he had done there I had to be aggressive and go all out for a birdie," Westwood said.
He did just that, hitting a drive and a five iron to the 450-yard 18th and holed out from 18 feet to take the mammoth first prize of pounds 183,340.
Clarke did not birdie the 17th so needed a two at the last to tie, but he hit the green to the right of the pin with his second shot and though he knew he could no longer win the big Irishman holed a 25-foot putt to finish just one stroke behind.
"Clarkie made my heart jump when he holed that long one but luckily I made birdie there just before him. We are great mates and Darren was the first to shake my hand," said a cheerful Westwood.
Clarke, who won the Benson and Hedges tournament only two weeks ago, was sporting in his praise of Westwood.
"I tried to make it tough for Lee and I made a good start, but a couple of bogeys at the sixth and eighth cost me my momentum. Lee did fantastic to make three under the cosh because he knew I was coming after him. It's nice to have this rivalry and I hope we can chase each other in the Order of Merit."
Clarke has now gone from seventh to fourth in the Order, while Westwood has jumped from 18th to sixth. Both are ahead of Colin Montgomerie, who finished here 10th on 273.Reuse content