Olesen continued to impress in his first start for three months following his recovery from hand surgery, adding a 68 to his opening 65 to claim the outright lead ahead of Pelle Edberg on nine under par.
But Colomo earned his share of the headlines at the Heritage Golf Club as he became the first player in the history of the European Tour to make a hole-in-one at a par-four.
The Spaniard arrived on the tee at the 329-yard ninth – his last hole – needing a birdie to make the halfway cut having dropped a shot at the eighth.
He opted for an aggressive approach and hit a high fade with his driver, and the bold move paid off as his ball bounded straight into the cup for a dramatic albatross.
“For the first time in my life I hit an unbelievable driver, very high with a little cut,” said Colomo after signing for a 69. “I tried to stop the ball on the green and the ball found the hole.
“I needed a birdie to make the cut, so a double-eagle is just fantastic.??I made a three-putt bogey on eight and I was two over and I needed birdie to make the cut. That???s why I hit driver as I needed a birdie.
“We couldn???t see it go in. We heard some guys shouting but we couldn???t believe that. We thought the ball was very close but when we were on the fairway, we couldn???t see the ball on the green. And then one guy told me that the ball was in the hole. It was a perfect shot.???
Meanwhile, Olesen got off to a shaky start with bogeys at the first and third, but the Dane responded with a remarkable run of five birdies in six holes and offset another dropped shot at 13 with his sixth birdie of the day at 16.
“I have read the greens very nicely this week,” Olesen said. “I missed a couple of putts in the beginning today but then I holed some really nice putts and I feel like I have the pace of the greens.
“I???m really looking forward to the weekend. It???s been a long break and then all of a sudden I???m up there in the lead, so it will be a lot of fun. I didn???t have the biggest expectations this week but I knew I was swinging the club well and I???ve been practising hard the last couple of weeks.
“I was obviously hoping for something good, but I???ve been surprised at how good my short game has been. I thought it would be the part that would be rusty, but it has actually been really good. I???m pleased at that and it???s brilliant to be leading. It???s fun to be out there and be at the front again.???
Edberg carded four birdies and an eagle at the seventh in a five-under 66 that swept him into outright second place ahead of young Englishman Matthew Fitzpatrick, who recovered from a double-bogey at 17 with a birdie at the next before he closed out a 67 with three birdies in his last five holes.
???To fight back after the double-bogey and still finish four under is very pleasing,” Fitzpatrick said. “It was steady and solid after that. I???m not too far off the lead. A two-shot swing can happen in a round or even on a hole here.”
Fitzpatrick shares third on seven under with South African pair Thomas Aiken (66) and Dean Burmester (68), while their compatriot and pre-tournament favourite George Coetzee is four off the pace after a 67.