Oxford ended a run of three successive home defeats in all competitions as Josh Ruffels' last-gasp strike lifted the U's to a 1-0 win over Doncaster at the Kassam Stadium.It seemed the hosts were going to rue Jack Payne's missed penalty in the 79th minute but, deep into added-on time, Ruffels spared his team-mate's blushes with a superb long-range strike.Oxford thought they should have been awarded a spot-kick early on for a foul on Wes Thomas while James Henry's first-time effort forced Rovers goalkeeper Ian Lawlor to tip round the post.At the other end, Tommy Rowe and Andy Butler might have done better with headers from set-pieces.Doncaster's best chance came when Rowe's shot just before the hour mark hit the right post and rolled along the goal-line.Oxford were gifted a golden opportunity to break the deadlock when Payne was brought down by Andy Butler just inches inside the box.Payne picked himself up to take the spot-kick, but struck it too close to Lawlor, who saved well to his left.It looked like the spoils would be shared but midfielder Ruffels hit a low left-footed drive from 25 yards that beat Lawlor at his left post in the sixth minute of injury-time, handing Oxford a victory that moved them up to eighth, five points adrift of a League One play-off spot.