Colsaerts ended up with a 9-under-par 64 Thursday and is four strokes ahead of Thomas Aiken, Branden Grace and Tom Lewis. Four players, including Louis Oosthuizen, finished tied at 4-under.
Colsaerts started slowly, with a birdie and a bogey leaving him even after seven holes. But he ran off four consecutive birdies over Nos. 8-11, had a birdie at 13 between pars at 12 and 14 before closing with four straight birdies.
"This is probably the best of my life. It's a serious test of golf," Colsaerts said. "I think the longest putt I holed was from 12 feet on the second."
Lewis's share of second came despite a double bogey 7 at the 16th hole and Grace overcame back-to-back bogeys at 3 and 4 en route to his 68. Aiken had a relatively quiet six birdies and one bogey on the day.
The Volvo Golf Champions is an exclusive event that includes winners from the European Tour last year, players who won the first two tournaments on the 2012 schedule -- Grace and Oosthuizen -- and current tour members under the age of 50 who have won more than 10 tournaments. The 2012 field includes 35 players.