Manager Nathan Jones credited his team for their professional performance as they avoided a cup upset to reach the fifth round of the FA Cup.
The gaffer made eight changes in the hopes of progressing and his gambles proved to pay off, with goals coming from Reece Burke, Carlos Mendes Gomes and Admiral Muskwe.
Speaking after the match, Jones said: "It's a tough place to come, it was a cup upset on the cards but I thought we were thoroughly professional. Cambridge are a good side that are doing really well, Mark Bonner is doing a great job but I thought we were really professional. When we had opportunities we took them and I think with a bit more quality, we could have had more.
"To come here, keep a clean-sheet and make eight changes, we've also had a few debuts, we've given game time to the players that needed that and they were able to come through it. It has been a good weekend."
Despite making wholesale changes it was a strong, competitive Luton side that ensured they would reach the fifth round for the first time since 2013.
"The front two played against Bristol City the other day, Gabe (Osho) has been doing fantastic, and the back three apart from (Dan) Potts have been playing week in, week out. Fred Onyedinma we played a lot of money for and Pete is a right-back we have a lot of hope for so it was a strong side.
"In the midfield area we had to play Carlos (Mendes Gomes) out of position and we gave Elliot (Thorpe) his debut and that was probably where we were gambling, but they've showed that they can cope."