Denmark's Lucas Bjerregaard claimed a three-shot lead at the halfway stage of the BMW Masters after overnight leader Sergio Garcia suffered a costly lapse in concentration in Shanghai.
World number 11 Garcia was one shot clear after an opening 64 and initially remained out in front on Friday thanks to birdies on the third, sixth and seventh at Lake Malaren.
However, the 35-year-old Spaniard then three-putted the 12th and ran up a double-bogey seven on the 13th, pulling his attempted lay-up into the water and taking three to get down from just short of the green.
A birdie on the 15th repaired some of the damage but a second round of 71 left Garcia nine under par and joint second with Thailand's Thongchai Jaidee, three behind the in-form Bjerregaard, w ho carded a second consecutive 66.
"It was definitely much tougher today and I still felt like I left at least three or four shots out there," Garcia said. " But it was obviously difficult. If you didn't hit the right shot at the right time you could pay the price and I definitely did a couple of times.
"I made a really nice par on the 17th and a great four on the last, which is playing very difficult so I'm not too upset, but I would have loved it to be a little bit better.
"H opefully it will be the worst round of the week for me, and then it should be okay. If not, then we'll have to find something."
Bjerregaard, who birdied five of his last eight holes for an inward nine of 31, is chasing his first European Tour title after finishing second to Justin Rose in the Hong Kong Open three weeks ago.
Before then, his previous experience of being in contention came in December's Alfred Dunhill Championship, when he slumped to a closing 89 - including a back nine of 50 - to slump from second to 49th.
"It was nice in Hong Kong to prove to myself and to everyone else that I can still compete up there," the 24-year-old said. "Hopefully I can do that again this week and just come up one place better than last time.
"I t was a great round today and obviously finished off with some good birdies coming in. Nothing much really happened on the first nine, just played really solid. But I thought it was a good bit tougher than (Thursday) with the wind up. Some of the holes were playing really long."
Ian Poulter carded a second consecutive 68 to join fellow Englishman Paul Casey and BMW PGA Championship winner Byeong Hun An on eight under, with Ross Fisher - who lost out in a play-off 12 months ago - another shot back alongside American Peter Uihlein.
Uihlein, who was playing alongside Bjerregaard, shot a 66 which featured seven birdies in succession from the 15th, the former rookie of the year narrowly missing from 15 feet on the fourth to make it eight in a row and equal the European Tour record.
With Rory McIlroy not competing, his rivals in the Race to Dubai have the chance to overtake the four-time major winner in the standings. England's Danny Willett just needs to finish 28th or better in the 78-man field, while Shane Lowry, Louis Oosthuizen and Rose must finish second or better and Branden Grace requires a win.
Rose could only add a 72 to his opening 67 to remain five under, with Willett and Oosthuizen three under, Grace two under and Bridgestone Invitational winner Lowry one over after a 75 which included a triple-bogey six on the sixth.