Peter Hanson fired a sparkling eight-under 64 to take a two-shot lead at the halfway mark of the BMW Masters in Shanghai.
It did not look as if it would be the Swede's day when he bogeyed the opening hole but he then poured in nine birdies in 13 holes to race to 14-under.
However, Hanson has the ominous figure of world number one and Ryder Cup colleague Rory McIlroy breathing down his neck.
McIlroy did not put a foot wrong in round two and his bogey-free round of 65 lifted him into clear second place, three in front of Robert Karlsson, who matched the 64 of his fellow Swede Hanson.
Overnight leader Jamie Donaldson came back down to earth after his opening 10-under 62 and a two-over 74 saw him slip six off the pace. He is now on eight-under alongside Justin Rose, Shane Lowry and Alex Noren.
Luke Donald is a further shot back on seven-under - seven back - after a 67 while Lee Westwood and Ian Poulter also have much work to do on the weekend after both carded 69s to end the day on five-under.
Medinah team-mates Hanson and McIlroy will be the final group out on Saturday and the Swede joked: "It's going to be fun playing 30, 40 yards behind him in the fairway but hopefully I can give him a good match.
"He's going to be a tough guy to beat, especially around this golf course."
McIlroy won the Shanghai Masters on the same Lake Malaren course 12 months ago and is seeking his fifth victory of the season.