Deon Burton scored his fourth goal in four games as Scunthorpe won at Oxford to move up to second in League Two.
The 37-year-old headed in Marcus Williams' cross, but later had a penalty saved by Ryan Clarke after Deane Smalley handled in the box.
Oxford, beaten at home by Plymouth on Boxing Day, fell further behind when David Syers fired the second.
And their best chance went begging when Sam Slocombe upended James Constable, but saved Smalley's spot-kick.
Slocombe was perhaps fortunate to only receive a yellow card for the initial foul, but dived to his left to keep out Smalley's shot.
The victory, Scunthorpe's fifth of the season away from home in the league, extended their unbeaten run to seven games and was achieved despite the absence of suspended top scorer Sam Winnall.
It put them level on points with leaders Chesterfield, who stayed top because of their superior goal difference, while Oxford dropped from second to fifth, with manager Chris Wilder facing a job to lift his side for the New Year's Day fixture at Newport County.
VIEW FROM THE DRESSING ROOM
Scunthorpe United manager Russ Wilcox talking to BBC Radio Humberside:
"We weren't at our best in the first half - that's a certainty. Our passing at times was really disappointing but I want to focus on the second half.
"I thought the introduction of Michael Collins in there made a difference and got us playing a little bit more.
"I'm disappointed not to have scored more goals, we created some chances, and you know that at 1-0, even 2-0 it can be difficult to see out games.
"We're joint top going into the New Year and I don't think you can ask for much more."
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