The 29 year old, whose only top-ten finish on The European Tour came four years ago in Saint Omer, also dropped shots at the first and second and carded a three at the par five eighth, as well as firing four birdies.
"It was really good today and a great start for me,” said Karlberg. “It wasn't the best start to the round with two bogeys in the first two holes, but I managed to get things back pretty quickly and went on a great run near the turn and managed to turn it around.
"The eagle was the highlight of the day for me. I actually hit the drive a little too far to the right and then was thinking of hitting three wood at the green, but I knew if I hit it right then I wouldn't have a chance to hold the ball on the green.
"So I decided to lay up to give myself a good yardage which I did and then hit a perfect wedge that landed four metres behind the pin and spun back into the hole. It was one of those sexy ones that you just love to see going in!
"The game has been good. I finished fourth in Sweden but then had a couple of tough weeks in Austria and then the US Open but I have been preparing really well for this over the past three weeks and it feels good."
Qualifying School graduates Mikko Korhonen and Matthew Nixon were left tied for third after both completed three under par 69s.
As the afternoon starters began to reach the turn, it was China’s Liang Wen-chong posing the most significant threat to Karlberg’s lead.
Liang, whose only European Tour title came six years ago in Singapore, carded three birdies in an outward 33 as he continued the form that took him to third place finishes in Austria and India this season.