The City boss made 9 changes to face the Championship side, and recalled striker Georgios Samaras struck a 90th-minute winner to end his 8-month goal drought and spare City extra-time.
With City now in the last 16, Sven believes the Blues are ready for a tilt at league cup glory and he is expected to revert to a full-strength side for the 4th round.
"We're relieved to get through and that's the most important thing," said Sven. "I can't say that we played excellent football because I don't think we did.
"However, it was the first time this XI had played together, it's a clean sheet and we are through even if we can play a little bit better.
"I had to give some players who have not played much the chance to perform, I think it's the right thing to do," added the City boss.
"They learned a lot, and so did I, which is important to us for the future.
"We're going to do everything to go as far as possible in this competition, I can promise that to the fans."