Colsaerts was warmed up for the final after needing two extra holes in to get past 1999 British Open champion Paul Lawrie earlier Sunday, but still had enough left in the tank to also best the former U.S. Open champion.
It was Colsaerts' second title and first since last year's China Open. The win also marked his European Tour-best seventh Top 10 finish of the season.
McDowell had advanced after downing Rafael Cabrera-Bello 2-up in the morning semifinals. He also lost to Colsaerts in last year's Volvo World Match Play quarterfinals.