AFC Wimbledon manager Mark Robinson took little joy from his side's last-gasp win over Northampton in the Carabao Cup due to a "really poor" performance at Sixfields.
The Dons were second best throughout but snatched victory at the death thanks to Anthony Hartigan's long-range strike, which deceived Cobblers goalkeeper Jonny Maxted.
It is the first time Wimbledon have reached the third round in their history, but that was of little comfort to Robinson.
"I don't think I've ever felt so flat after a win," he said. "We didn't play well at all – that's probably the worst I've seen us in my time here.
"We got really lucky because Northampton were better in all departments and that's really disappointing because you won't get very far playing like that.
"It's nice to create a bit of history and get through to the third round but that's the only positive to come out of the game because we were really poor.
"I don't know why that was. I felt we would put in a good performance but we were so poor, both technically and tactically, and it just wasn't very good to watch. They were a lot better than us."
Northampton manager Jon Brady was pleased with his side's display despite the late defeat.
"All in all, that is the way we want to play," he said. "Yes, we need to put the ball in the back of the net a few times and we could have done tonight, but I thought our intensity was good from front to back out of possession and the way we closed them down was excellent.
"And then the way we played in possession, that's how we want to move the ball – we've just got to put the ball in the net.
"It was obviously disappointing to concede so late and Jonny knows he should probably save that, but we should stop it before they get that far so there are lessons to be learned."