In-form striker Junior Mendes struck his third goal in a week to put Mansfield on the road to a vital victory against promotion rivals Oxford.
Mendes, without a goal in 19 games just a week earlier, could have had a hat-trick in a one-way second half as the Stags leap-frogged United into fifth place.
Afterwards manager Keith Curle, who had seen his side clinch only their second win in seven games said: "Junior was at his best, that's what you get from him all the time.
"Great commitment, great energy and a desire to win. Overall the performance was spot on." Oxrford, with just one win in ten games, were punished for wasting three great chances in the opening five minutes.
New United boss Graham Rix, still looking for his first win at the club, had kept faith with young keeper Simon Cox.
And the keeper was unlucky to concede after just 16 minutes as Mansfield took the lead against the run of play.
Bobby Hassell's deep free-kick was eventually knocked back by Rhys Day to Tom Curtis whose powerful low drive was only parried by the unlucky Cox for Mendes to rifle in the rebound.
Three minutes later, Cox again had no chance as the Stags doubled their lead.
Jon Ashton's back-pass fell short and Colin Larkin nipped in, rounded the keeper and bent the ball into the roof of the net from an acute angle.
Earlier hesitancy by Day had almost let in Mark Rawle in the first minute, but the striker's low shot was easily held by Kevin Pilkington.
Less than 60 seconds later the U's again got behind the home defence, Chris Hackett's lobbed pass picking out Steve Basham whose half-volley was acrobatically tipped around the post.
Incredibly Oxford then squandered their third clear chance in the opening five minutes, Basham's clever pass releasing Dean Whitehead who prodded wide.
They were punished for the profligacy in front of goal when Mansfield then struck twice in four minutes.
However the visitors continued to play the better football and were rewarded in the 34th minute when Whitehead unleashed a 25-yard screamer into the top corner from a short corner routine.
But just two minutes later Mansfield restored their two-goal advantage, Day rifling in from six yards after Neil Mackenzie's 25-yard free-kick was blocked.
From then on Mansfield dominated and at the start of the second half Mendes wasted three golden opportunities to make the game safe, the best coming in the 65th minute when he was foiled by Cox's tremendous point-blank save.