Tommy Mooney scored the only goal of the game as Graham Rix's new look Oxford United side recorded their first win of the season in a thrilling League Two clash.
The game had it all - two red cards, a flurry of bookings, end-to-end goalmouth action and three goal-line clearances.
Mooney struck the game's decisive goal after 36 minutes, side footing home an inch-perfect cross from flying winger Chris Hackett.
Hackett caused the Mansfield defence no end of problems for the entire match, but so often the finish was not there.
And when defender Leo Roget was sent off for a professional foul four minutes after hal- time, you feared the worse for the home side.
But they defended heroically, throwing bodies in front of the ball and not giving the Mansfield strikeforce any time on the ball.
When they did get through the defence, they found goalkeeper Chris Tardif in fine form.
Visiting striker Colin Larkin twice made Tardif save at full stretch, and also forced defender Dave Mackay into fine blocks.
Mansfield did not help their cause when Lee Williamson saw red with 14 minutes to go and their chances of victory left the field with the midfielder.