Second-half goals from James Constable and Peter Leven earned the U’s a 2-0 win in their replay against Accrington Stan-ley.
The game took more than an hour to spark into life, but the hosts were good value for their win in the end.
Joy at setting up a third round tie at home to Sheffield United next month was tempered by frustration at the quality of the pitch.
Suffering the after-effects of London Welsh’s game on Saturday, the bumpy surface led to a host of bobbles which disrupted both sides.
Full back Damian Batt said: “I’ve been here nearly four years now and that’s the worst I’ve seen it.
“A few times the ball skidded off players and the crowd got frustrated, but I don’t think they realised just how difficult it was to play on.
“We did what we had to do and sometimes games are not as pretty as we’d like them to be, but we’re in the next round.”
Mickey Lewis felt it also played a part in Adam Chapman coming off with a twisted ankle and the U’s assistant manager was unhappy with the number of divots.
He said: “There was a rugby game here at the weekend, I don’t think I’m talking out of turn, but I think anyone who can see the pitch would say it’s not in the condition it was in last season.”
It is the first time in ten years that United have made it through to the third round.