Karlberg recovered from bogeys on his first two holes with five birdies and an eagle for a 5-under-par 67. Liang Wen-Chong and Simon Dyson are also at 5-under.
Matthew Baldwin, Javier Colomo and Alessandro Tadini are tied for fourth one stroke off the pace and six more players are at 3-under after the first round.
Liang had six birdies against a 12th-hole bogey for his share of the lead while Byron was bogey-free in the first round.
Karlberg's round was much more adventurous. After opening with bogeys at Nos. 1 and 2 he had back-to-back birdies at 6 and 7 to get back to even. He elected to play up on the 564-yard, par-5 eighth with his second shot. His wedge shot landed about 12 feet past the hole and spun back in for eagle.
He added a trio of birdies on par-4 holes, including on the 448-yard 18th.
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