Lee Westwood shot an 8-under 64 to lead by three strokes after the second round at the Nordea Masters on Thursday.
The third-ranked Englishman was at 12 under after playing with a new set of irons ahead of the U.S. Open at the Olympic Club in San Francisco next week.
"The conditions were perfect for low scoring, here was little wind and the greens were pretty pure," Westwood said. "I putted nicely and that has given me a lot of confidence.
"I could have been even lower, but I left the ball on the edge of the hole a couple of times."
Although ninth in Europe's 2012 Race to Dubai, Westwood is 57th in the European Tour's average putts per round.
"I am here building up all of my confidence," he said. "And the Olympic Club won't be any longer than this course, nor will the rough be any thicker. Maybe here only the fairways are a bit wider."
Peter Hanson of Sweden (68), Scotland's Lloyd Saltman (64) and Carlos del Moral of Spain (67) are next.
Saltman's round was his lowest on the European Tour and included an albatross at the par-5 12th.
"I heard a little clap and then there was a big roar as I started walking, so I knew it must have gone in," Saltman said.
First-round leader Magnus A Carlsson of Sweden followed up his 65 with a 72. Defending champion and countryman Alex Noren had been in danger of missing the cut following a 74 on Wednesday, but a 66 will ensure he plays the last two rounds.