The U’s opened the scoring just after the half-hour mark when Alex MacDonald slammed the ball home from close-range after Lenny Pidgeley was unable to claim a cross from George Baldock.
Matters got worse for Mansfield in the second half as MacDonald bagged his second goal of the afternoon after Pidgeley had done well to keep out an effort by Callum O’Dowda.
Any hopes of a comeback were all but extinguished shortly afterwards when Danny Hylton converted a spot-kick after Ryan Tafazolli had brought down Patrick Hoban inside the area.
Stags manager Adam Murray made one change to his starting XI with Jeffrey Monakana handed his debut in place of Reggie Lambe.
The Stags started with plenty of energy and had a promising opening in the second minute as striker Vadaine Oliver was unable to get any conviction on his header after defender Ryan Tafazolli flicked it on from Callum Elder’s throw.
Oxford went up the other end shortly afterwards and missed a golden opportunity as Callum O’Dowda’s corner from the right side picked out full-back Sam Long who blasted his shot wide.
A midfield battle began to transpire, as neither team was able to full assert themselves. The U’s had another good chance in front of goal as 30-yard pass from midfield found the head of Danny Hylton who forced a good reflex save from Lenny Pidgeley.
Midfielder Simon Heslop broke forward on the right side on the quarter-hour mark before blasting his shot towards goal, only for it to be blocked by defender Johnny Mulluns.
Mansfield’s youngster Jack Thomas received the first caution of the match after a late challenge in the corner on Jake Wright bought the ire of the referee.
After a scrappy period of play, the U’s broke the deadlock in the 31st minute.
After Lenny Pidgeley was unable to collect a cross put in from the left by George Baldock, Ritchie Sutton was unable to clear the ball to safety and forward Alex MacDonald pounced on the loose ball and placed it into the back of the net.
Oxford then had a good spell of possession and threatened to break the Stags defence on a number of occasions. O’Dowda operated successfully down the left wing and proved to be tough to handle.
As the first half came to a close, the Stags instigated some good build up play as the ball fell to Heslop on the edge of the penalty area. The midfielder took the ball in his stride and fired a strike towards goal, only for it to be deflected out for a corner kick much to the relief of U’s custodian Ryan Clarke.
The U’s continued to look dangerous on the counter-attack. Moments before the referee blew his whistle for half time, Josh Ruffels received the ball just outside the penalty area and unleashed a venomous shot. Oliver successfully managed his defensive duties on this occasion and produced a strong block to deny the midfielder.
The first half concluded with the home side leading the contest 1-0.
Early in the second half, MacDonald came close to adding to his goal tally as his shot from 30 yards went past a number of bodies. Pidgeley was called into action and made a good save low down to his right.
Tempers flared in the middle of the pitch on 52 minutes as Hylton was shown a yellow card after fouling a Mansfield player.
Oxford doubled their lead in the 54th minute as MacDonald added his second goal of the match. The ultimately successful play started as O’Dowda charged powerfully through the Mansfield defence and forced a smothering save from Pidgeley. As the Stags attempted to clear the ball, MacDonald found space and finished with aplomb into the top right corner.
Tafazolli was the next player to go into the referee’s notebook after a late challenge on striker Patrick Hoban.
The match situation got all the more difficult for the Stags in the 64th minute when the referee pointed to the penalty spot after Hylton was fouled by Tafazolli after lynching onto the ball. The striker stepped up to convert the opportunity and made no mistake, sending Pidgeley the wrong way to make the score 3-0.
The U’s were forced into a substitution after MacDonald suffered an injury. Young midfielder Kemar Roofe came on in his place. Mansfield followed suit shortly after when Billy Kee came on for Oliver.
With a quarter-of-an-hour to go, Hylton was lucky not to be sent of for a second bookable offence after he appeared to create a goal scoring opportunity deliberately handling the ball past Pidgeley. Hylton was substituted shortly after as fellow striking compatriot James Roberts came onto the pitch.
The Stags also made a change as Reggie Lambe came on in place of Junior Brown.
Substitute Roberts was in the thick of the action on a couple of occasions for the U’s, most notably after he charged down a Pidgeley kick only for it to rebound just wide of the left hand post to safety.
Mansfield’s attempts to push forward for a consolation goal through Lambe and Monakana proved futile as the match ended in a 3-0 win to the hosts.
Attendance: 6,954 (322 away supporters).