OXFORD United's wait for a point in Sky Bet League Two goes on as two players with connections to the club were on target to give Mansfield Town victory.
Former United midfielder Adam Murray bagged the winner two minutes from time as a poor game sparked into life late on.
It sunk the visitors, who had looked set to pinch the game after Danny Hylton came off the bench to score for the second game running.
His penalty cancelled out Mansfield's opener, scored in the first half by Ryan Tafazolli, who went on tour to the USA while on trial at United two summers ago.
Michael Appleton made two changes from the side which started Tuesday's Capital One Cup win at Bristol City.
George Long replaced Max Crocombe in goal, while Michael Collins came in for Josh Ruffels, who was fit enough to be among the substitutes.
The U's were hoping to pick up where they left off at Ashton Gate, but did not get going in a first half desperately low on quality and notable incidents.
Mansfield worked hard to limit the visitors' time on the ball and when they won possession back, they were very direct.
Both defences dealt with what was thrown at them with few problems.
It took a mistake to create the first chance, on 18 minutes.
Long made a mess of bowling the ball out from the edge of the box, presenting it straight to Ritchie Sutton.
United were relieved it did not go to a more attack-minded player, as the centre back rushed his lob, which did not threaten the goal.
On the half hour mark a clever flick-on from Chris Clements teed up Sam Clucas, whose looped finish was just off target.
The dour stalemate was broken six minutes before the break.
Long got fingertips to an excellent free-kick from Clements, diverting the ball on to the inside of the post, where it bounced back across goal for Tafazolli to head in.
Falling behind briefly stirred a reaction from United before the break.
Carlton Morris, often an isolated presence up front, was picked out by a David Hunt throw and the striker's shot on the turn was parried by goalkeeper Sascha Studer at the near post.
United had work to do at the break, but their arrears were almost extended on the stroke of half-time, when Tafazolli headed narrowly wide from a Clements free-kick.
The visitors were sent out early for the second half, but it got no better for them when play restarted.
A careless back pass from Jake Wright almost put Long in trouble, but Clucas was unable to capitalise.
The striker fared better just before the hour mark, when he cut inside and curled a shot just wide.
United desperately needed some inspiration and Appleton looked to his bench for a spark.
Alex Jakubiak came on for his debut and instantly the visitors carried more of a threat.
But it was only after Hylton was introduced in the final quarter of an hour that they caused Mansfield problems.
Just two minutes after coming on, the striker latched on to an excellent threaded pass from Michael Collins.
Hylton shielded the ball well and lured Tafazolli into a lunge, conceding a penalty.
United's No 10 dusted himself down and although Studer dived the same way, the ball found the corner of the net.
Buoyed by the goal, the visitors went in search of a winner in the final ten minutes.
Jakubiak headed a decent chance over, while Brown had a shot well saved.
They looked the more likely to score, but two minutes from the end of normal time Mansfield grabbed the winner.
A cross to the back post was not cleared and no-one tracked Murray, who ran on to the loose ball and fired a low shot past Long.
It was the decisive moment and ensures United, who visit Morecambe on Tuesday, are one of five teams in League Two yet to get off the mark.
Oxford Utd: G Long, Hunt (Jakubiak 60), Mullins, Wright, Newey, Collins, Meades (Ruffels 71), Riley, Potter (Hylton 76), Brown, Morris.
Unused subs: Crocombe, Raynes, Rose, O'Dowda.
Mansfield: Studer, Sutton, Dempster (c), Tafazolli, Beevers, Taylor, Clements (F Bell 85), McGuire (Murray 85) Heslop, Fisher (Palmer 68), Clucas.
Unused subs: A Bell, Jones, Marsden, Thomas.
Referee: Richard Clark (Northumberland).
Attendance: 3,042 (405 visitors).