Cody McDonald's first-half winner brought Gillingham their first away win in 18 months with a 1-0 victory at Oxford.
The striker, on a season-long loan from Norwich, bagged his fifth goal of the season in the 40th minute when pouncing on a weak backpass from Oxford's new captain Jake Wright.
McDonald rounded keeper Ryan Clarke and slotted home with ease.
It was a lead Andy Hessenthaler's team, who had not won for 30 away league games, thoroughly deserved.
Charlie Lee also went close with a first-time effort and both Chris Whelpdale and Charlie Lee planted headers wide.
Oxford improved in the second half when top scorer James Constable came on to offer striker Steve Maclean some support, but with so many changes in recent weeks, they still lacked their opponents' teamwork and understanding.
Gills keeper Alan Julian pushed Alfie Potter's shot on the turn around a post, and beat out a fierce drive from Steve Maclean after industrious play by Constable.
Simon Clist had a free-kick tipped over, and Tom Craddock drilled a shot wide late on.
The Kent side defended well to hold out, but out-of-form Oxford, who slipped to their fifth straight defeat, were booed off by their fans at the end.
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