Gillingham manager Andy Hessenthaler praised a "siege mentality" as his nine men saw off the threat of Oxford with a 1-0 win.
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.
Hessenthaler said: "I thought we were terrific. It was a siege mentality when things were going against us.
On the dismissals, he added: "We made some poor decisions as individuals.
"It was backs-to-the-wall stuff and hopefully we have opened a few people's eyes.
"It shows people what spirit we have within the camp and I tell people to wear the shirt with pride, and every single one of them did that."