Speaking to the club website, Dowie said: "We were patchy at best and Millwall deserve an enormous amount of credit.
"They went 4-5-1 and it gave us plenty of problems but we did have some good opportunities to break and we got the job done without being fluent. I think we deserved that after last week where we had about 26 shots on goal and lost."
"It was important for us to get the lead. "I thought we'd kick on from there but we didn't really do that and we started to look a bit nervy. "But like I said, Millwall deserve a lot of credit for the way they came here and made it very tough for us
"To be fair to us, we only had one defender playing in position in the back four and we were down to the bare bones. "We looked edgy at times but we're in the hat and to get into the last 16 is a big thing. It'll be interesting to see who goes out before the draw is made."