Millwall boss Neil Harris has bemoaned the "cheap" goal which settled Sunday's Sky Bet Championship encounter with Rotherham United at the AESSEAL New York Stadium.
Sean Raggett's 20th-minute header proved to be the only goal of a game in which The Lions dominated possession but were unable to score.
The boss told millwallfc.co.uk that it is "extremely disappointing" to have left Yorkshire this week with no points from a possible six.
"I'm frustrated, I've got to be honest. Rotherham did nowhere near enough to win the game against us," he said after watching The Lions gain over 60% possession of the ball against The Millers. "That's twice in four days we've thrown points away.
"Ultimately, when you play against Rotherham you know you've got to stand strong against set-piece deliveries and for the majority of it, we did. But, for that one moment we get it wrong. We don't compete, we make bad errors of judgement and the ball ends up in the net.
"It's extremely disappointing to have two games in Yorkshire and to come away with nothing. That's twice in four days our fans have had to travel a long way to see us give away cheap goals and we've not affected the ball going the other way with enough quality."
The manager went on to describe how it is imperative to not give teams a "leg-up" in the Sky Bet Championship.
"We used the ball well the majority of the time but I would've liked to have seen us have more clear-cut chances and be a little bit better in the final third. I never felt in danger from Rotherham otherwise, apart from one save from a counter-attack.
"What we've learnt from the last four days and last year so harshly at times is that you cannot give teams at this level a leg-up. If you give them a chance to score cheap goals then you chase the game and it's very difficult."