Oxford boss Chris Wilder was left to rue his side's poor finishing as their eight-game unbeaten run ended with a 1-0 loss at Gillingham.
Joe Martin, for two bookings, and Lewis Montrose, who lashed home on the stroke of half-time, were both shown red by referee Gavin Ward for the home team while the visitors missed a glut of chances in both halves.
Wilder said: "Up to the goal, we absolutely dominated them. We controlled every part of that game and had the chances to show for it.
"But that's where games are decided and yet again we have missed some fantastic opportunities to put us in the lead.
"We had 20 opportunities on goal again but that's the disappointing thing - we just need to be a bit more patient.
"Their goalkeeper has made some fantastic saves. It is a bit like a broken record and it is a bit disappointing but I know we are on the right track."