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Manager Neil Harris admitted his Gillingham team were second best in every department during a first half where Mansfield all-but wrapped the game up.
The Stags led 2-0 at the break, and it could have been more, before they then eased their way to the full-time whistle which was greeted by boos from Gillingham's fans.
Harris, who took stick himself at the full-time whistle from some frustrated supporters, said: “Mansfield deserved to win the game for sure, they were better than us in the first half, in all aspects of the football match.
“Our use of the ball and our delivery from set-plays was really poor, then ultimately we didn’t defend our box and in the first half against a big physical team, they out-run and out-fought us, obviously it pains me to say it but everyone who was there could see it, in the first half. It was not a lack of trying from the lads, never that, it (was) just that we couldn’t stand up to it.
“I was angry at half-time with the way we performed in the first half but watching the goals and watching some clips back, they (Mansfield) are just very good at what they do, they play forward and they run forward and they run over the top of you, as much as it hurts to say it, they ran over the top of us. I can’t accept it but the group has to try and be better than that, it happened at Tranmere and it happened here, against two big physical teams.
"Disappointed, frustrated, all of the above, ultimately in the first half, we fell short.
“It wasn’t about shape, it was about being out-fought. A better League 2 team beat us.”
The match followed a minute's silence to mark the passing of the Queen and was followed by a rousing rendition of 'God Save The King' but Gillingham fell flat when the game kicked off.
Mansfield bossed the opening 45 minutes and Gillingham let in two goals during that half. Keeper Glenn Morris saved a penalty in between those. There were other chances where Mansfield came close to extending the lead.
Harris said: “I said quite a lot at half-time that will stay behind the four walls of the changing room, this was a monumental occasion for the country and the football club. A lady (Queen Elizabeth II) gave great service to the country with real bravery and we didn’t match that bravery.
“Physically, we got beaten up. Adjustments can be made, we readjusted at half-time, second half was better but still we weren’t much of a threat second half.
“It is tough. I will watch the game back. I won’t say what I said to the players and what they will be doing tomorrow (Sunday) but the players have to understand frustration doesn’t just end at the dressing room door, it affects me and my family and 5,000 people that pay money to watch, if the players don’t perform then they have to take the punishments that come with it.”
Co-chairman and chief exec Paul Fisher was among those in confident mood ahead of the game.
Prior to the weekend, he wrote in his programme notes: "We are moving in the right direction and it only takes a couple of victories for things to look very different.
"Teams have had slow starts in the past and gone onto mount promotion challenges, and there is no doubt in my mind that we are well placed to do the same."
But following the 2-0 defeat, he tweeted afterwards: "Worst performance of the season and so so disappointing after the last two games. We have to improve and quickly!"