The 34-year-old played almost immaculate golf for the second day running on Friday, a second successive 64 helping him charge four strokes clear of the field with a 14-under-par total of 128.
England's Eddie Pepperell returned a 66 to climb into second position on 132, one ahead of Thailand's Kiradech Aphibarnrat (67).
It was Colsaerts, however, who stole the spotlight although he acknowledged that he had to work a bit harder in his second round than he did on Thursday.
"Yesterday it was kind of eyes closed and everything kind of falling in my lap," he told reporters at the Regnum Carya Golf and Spa Resort, which overlooks the Mediterranean.
"Today it was actually more satisfying to shoot the same score but having to go and find it a little bit more. I recovered well every time I hit a bad shot so I guess that was a key.
"I wasn't quite as good off the tee, I thought, but I still played some great shots into the greens."
RYDER CUP
Colsaerts has won twice on the European Tour, at the 2011 China Open and the 2012 World Match Play Championship in Spain, and said he would be taking nothing for granted over the weekend.
"If I'm capable of going 14-under in two rounds then somebody else, or a few other guys, are capable of doing the same," he explained. "There are a lot of great players playing in this tournament.
"I'm just going to try to keep playing the way I've been playing the last two days. Probably not get ahead of myself and see where that takes me."
Sharing fourth place on 134 were English pair Matthew Southgate and Matthew Fitzpatrick, Ireland's Shane Lowry and Scot Stephen Gallacher.
World number six Justin Rose, the highest-ranked player in the field, was on 135 after carding a 68.
"I didn't play particularly well," the Englishman said. "The short game kept me in it a few times early on the front nine and on the back nine I couldn't quite capitalise on the couple of chances I had.
"The last few holes are pretty tricky here. You've got to play good golf coming in."
Eighth-ranked Henrik Stenson of Sweden has struggled for form and is tied 62nd on 144. England's Tommy Fleetwood, the runaway money-list leader, was on 141.
(Editing by Christian Radnedge)
