Lincoln's play off hopes suffered a blow as they crashed to their first home defeat since November against fellow promotion contenders Oxford United.
The Imps were always in trouble after conceding an early goal and despite plenty of effort were well beaten by the U's.
The winning goal came after just four minutes when Andy Scott exchanged passes with Dominic Foley before firing a left foot shot into the top corner.
Scott almost scored again two minutes later when he was inches away from converting a cross from Matt Robinson as the Lincoln defence stood off him.
Lincoln looked to hit back but despite winning 10 first-half corners never really troubled Andy Woodman.
There best chance fell to Simon Weaver who sent a header over the bar after United keeper Andy Woodman punched a clearance from one of his own defenders off his line.
Six minutes before the break the U's almost doubled their lead when midfielder Dave Savage picked out Foley with a cross but the striker headed wide of the post.
Ben Futcher put a second half header wide and substitute Simon Yeo headed over from close range.
But Oxford always looked the more likely team to find the net again and went close in the 89th minute. Scott rose above the home defence to meet a flick on from Jefferson Louis only to be denied by an excellent one handed save from Alan Marriott.
Lincoln manager Keith Alexander said: "I cannot fault the effort but we did not have enough quality when it mattered. We never looked like scoring. " Ox ford boss Ian Atkins said: "It was an important win for us. Lincoln have still to play five of the teams at the top and will cause them problems. "