The South African side briefly took over at the top of the table at the weekend with their 40-22 home win over the Stormers. Cullen then had to wait for a second half revival at Cardiff Arms Park to turn a 15-12 interval deficit into a 33-20 bonus-point win to return to the top.
“We made a really good start, scoring two tries in the first 10 minutes of the game, and had some other chances. But fair play to Cardiff, they dug in really well and threatened on a few different occasions,” said Cullen.
“At half time, it was ‘Oh, we are in a proper game here now’. It wasn’t just we had fallen behind, but that Jordan Larmour was in the bin.
“We started the second half well, stayed composed and played the game in the right area. As the game went on, the guys who came off the bench added well.
“I’m pleased to get a win, but there are lots of things we can get better at as well.”
It proved to be a dream comeback for prop Michael Milne, who came off the bench and scored two second half tries on what was his first appearance of the season after injury. Fellow front row replacement John McKee got another second half try, while Rob Russell and Max Deegan crossed in that opening blitz.
“It has been a nice four weeks for us. There was a break post Champions Cup and all the attention went to the Six Nations.
“We had a good chunk of guys away, so it was good for us as a group of coaches to work with the guys we had, some of who were a bit frustrated with the time they’d had.
“The game against Saracens was a big step up, but a worthwhile exercise for us and we will do something similar with Bath to lead us into the game against Zebre.”
With a four point lead over both the Bulls and third-placed Glasgow Warriors, Leinster now have seven games to play to hold onto their position to earn home ties in the knock-out phase.
“I watched the Bulls and they look pretty powerful. They will be coming to the RDS two weeks after the Six Nations,” added Cullen.
“We then go to South Africa in between the quarter and semi-finals of Europe. Our international guys will be back by then and we’ll have to manage them well.