Wrexham edged their FA Cup replay against Cambridge to book a second-round trip to Brentford on 3 December.
After a tight first half, Mathias Pogba put Wrexham ahead as he flicked Curtis Obeng's dangerous ball into the net.
Obeng also laid on Wrexham's second with an even better cross from the right, allowing Danny Wright to head home against his former club.
Michael Wylde headed a late goal for Cambridge, diverting James Jennings' cross, but Wrexham held their nerve.
The first meeting between the two sides finished 2-2 and the Blue Square Bet Premier rivals again looked matched over the first 45 minutes at the Racecourse Ground.
Either team could have broken the deadlock in the opening 20 minutes, with Joe Clarke seeing a shot deflected wide for Wrexham and Cambridge striker Michael Gash firing wide from close range.
But league leaders Wrexham asserted themselves after the break to book their trip to League One promotion chasers Brentford in the next round.
Pogba had been a thorn in the visitors' side and got the goal he deserved in the 59th minute, latching onto an Obeng cross before the same defender set up Wright in the 76th minute.
Wylde gave Cambridge a glimmer of hope with three minutes left, nodding home a Jennings cross, but it was too little too late for Jez George's young charges.
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Cambridge United manager Jez George told BBC Radio Cambridgeshire:
"We're out with much frustration and disappointment.
"When you look at it overall they're a good side. I thought in the first 45 minutes they put us under no end of pressure.
"But we dealt with the ball played forward early. I think we had the best chance of the first 45 minutes even though we were under the cosh for most of it.
"The most frustrating thing for me is they never came out in the second half. We bossed the first 10-15 minutes of the second half and they score the first goal."