The hot run over holes 11-16 allowed Colsaerts to finish the day at 7-under-par 65. Ricardo Gonzalez and Maximilian Kieffer also shot 65 and are tied with Colsaerts for the lead.
Colsaerts opened his tournament on the second nine of the Golf Club Torino with a bogey before running off six straight birdies. He added another birdie at the 18th and then had eight straight pars before closing with a birdie at the ninth for a 65.
Kieffer had four birdies on each side, offset with a bogey at the 427-yard, par 4 11th.
Gonzalez began his day birdie-bogey but made the turn at 2-under. He jumped up the leaderboard with an eagle at the 531-yard, par 5 12th and had three birdies over Nos. 14-17.