While Colsaerts followed his opening career-best 62 with a level par 70, the 28 year old from India moved to eight under par at Hilversumsche Golf Club after a round of three birdies and a solitary bogey.
"I hit the ball quite well - I suppose you could always have a couple of shots better," he reflected. "It would have been nice to birdie the 18th but overall I am happy.
"The conditions are getting tough now so I should be near the lead by the end of the day and a good round tomorrow will keep me up there."
Colsaerts, the longest driver on The European Tour this season, lost a ball in the heather at the 476 yard sixth - his 16th - which cost the 27 year old a double bogey six.
"We had to wait a while on the tee and I didn't have the same rhythm but at the end of the day I just didn't hit a good drive and it went left into the long stuff," he explained.
"But I did well to make a par with the second ball because it is a tough hole so a double with losing a ball was as good as I could do. I could easily have dropped another shot and then you are in trouble."
He birdied the next but again relinquished his lead on the eighth - his last - when he chipped ten feet past the hole and missed the return putt.
American Todd Hamilton's decision to join The European Tour could bring him a first victory since the 2004 Open Championship this weekend.
The 44 year old, now down at 545th in the Official World Golf Ranking and with only two cuts made in his last 19 events, is just a stroke behind along with Swede Christian Nilsson and France's Jean-François Lucquin.
Hamilton, seven under par after rounds of 66 and 67, said: "I don't have full status on the US Tour any more, so I looked at the schedule and thought I'd come to places I've never been to.
"I had never been to Switzerland and it was great, never been here and its great and then we have Austria and France in the next two weeks which are another two places I have never been.
"I will then play Singapore and Hong Kong towards the end of the year to make up my 12 events.
"I didn't hit a lot of fairways, but it seemed like I always had a good angle to the flag and everything worked out."
Former Saint Omer Open winner Nilsson's 65 included an eagle at the 484 yard par five 12th.
"I'm very happy, I've been struggling quite alot the last couple of weeks so it felt really nice to have a good round," he said.
Lucquin has been on a miserable run of form this year and is only 198th in The Race to Dubai, so the former Omega European Masters champion was delighted to rediscover his game.
He said: “Finally I am going to play the weekend! I haven’t made a cut for three months so this is a great relief for me let me tell you.
“It is very discouraging when you go through a period like that but I tried to do my job, work on the range and hopefully it had turned around for me and I can have a good weekend.”
German Martin Kaymer, who in his first tournament since winning the US PGA Championship title has started with two 67s to be just two behind.
He said: "67 was a reasonable score today - it wasn't the score that I was hoping for because I had the good conditions on the greens this morning but the score is okay.
"I am playing well - I just need to the putts to drop. The same thing happened in the PGA Championship actually, I didn't make a lot of putts for the first couple of days but I tried to be patient and collect my pars and keep giving myself chances for birdies which I did and then they started to drop over the weekend."