United were held to a goalless stalemate by the Dons, meaning the two sides must meet again at Glanford Park to decide who progresses to the second round.
“I think you've got to give credit to Wimbledon, they stepped forward in the second half,” he said.
“They came out and took the game to us a little bit more and once we readjusted and found ourselves, the game probably got a little bit too open, and Wimbledon kept coming at us.
“We made three defensive changes as well and I was pleased when they came out straight away and worked quite well as a unit.
“But it is an intimidating ground. It was a proper cup tie, as soon as we walked out, the fans were up for it, and we knew it was going to be a difficult task. But it's by no means over.
“The biggest thing is to come away from home and keep a clean sheet, unfortunately we haven't got a goal.
“That's why we get frustrated, because we know what we're capable of doing.”
Terry Brown, the Wimbledon boss, conceded his side were lucky to still be in the competition.
“We hung in there, we did probably create the best chance of the game late in the first half and had we put that away then possibly it might have been different,” he said.
“But we came out in the second half and worked our socks off and I was really proud of them. They stuck to a game plan, we had to contain them, they're full of quality players.
“We were trying to exploit some of their weaknesses and take advantage of some of our strengths. We got the ball to our wingers in the second half and got the ball in behind Scunthorpe.
“We can play a lot better than that and we'll need to when we go up there.
Scunthorpe's movement upfront and in midfield was the best we've played against this year, so to contain that, I've got to be happy.”