Daryl McMahon admitted Ebbsfleet were beaten at half-time after blowing a two-goal lead against Doncaster in the FA Cup.
Goals from Danny Kedwell and Luke Coulson had Fleet in charge against their League 1 visitors when the fourth official put the board up to show two added minutes at the end of the first half.
That was enough time for Tommy Rowe and John Marquis to score, sending the sides into the break level.
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Manchester United so often scored goals in 'Fergie time' and the trait seems to have been passed down by Sir Alex to his son Darren, now the Doncaster manager.
McMahon said: "That was the critical bit of the game and we lost the game then. Even though it was level at half-time, the disappointment of being two up and then 2-2 changed my team talk, changed Darren’s team talk at half-time and the game became difficult then for us.
"We showed, for 45 minutes, we’ve got players that have the technical quality of players in League 1 but what we didn’t have was the professionalism of seeing that last two minutes through. It’s a lesson we have to learn, going forward in our league campaign.
"We have to be a bit more professional, ruthless, clinical to make sure that in those two minutes they don’t score. Kick the ball out of the ground 10 times if you have to, get to half-time at 2-0 and then we’ll go again from there.
"We were so good for 45 minutes as well, defensively, shape, breaking well and just for that two-minute period you switch off and they score.
"They’re a League 1 side, we’re a National League team, evolving, hopefully and trying to get into higher levels but we have to learn that you have to do your job for 47, 49, 50 minutes, whatever it is, not just 45."
Fleet were in dreamland for a matter of minutes after Kedwell converted a penalty and then provided a classy assist for Coulson to run on and make it 2-0.
The ground was rocking with the home crowd believing their side might be on their way to claiming a first Football League scalp for more than 20 years.
McMahon said: "Everything we worked on was about having good shape and breaking out with Coulson in the pocket. Weston and Cook can travel with the ball and it worked very well for 45 minutes.
"The lads were were absolutely outstanding for 45 minutes but that last two kills your game.
"It is difficult, from being in that winning position of 2-0, I know it’s only half-time but mentally, for a footballer, you’re 2-0 up and then you’re 2-2 against a side who are better than us.
"You let that 2-0 lead slip and it makes it difficult for you to recover and I don’t think we did.
"We need to be a little bit more professional and do our jobs properly for the whole time. It’s so important that you don’t switch off, especially against a League 1 side. We’ve been taught a lesson in terms of that.
"When you look at games sometimes you might think ‘I might be better than that player at that level’ but you see in the details when you play against them that they do their job the whole time, for 90 minutes and don’t switch off.
"The second half was difficult to watch, especially when Bushy went off, down to 10 men but we have to learn and get on with it."