Valerien Ismael was frustrated by a 'completely stupid mistake' for Swansea City's second goal as Barnsley lost 2-0 at home on Saturday evening.
The Reds were on top in the first half but conceded seconds before the break then a calamitous mix-up allowed the Welsh side to make it 2-0 early in the second half.
Head coach Ismael said: "It was a very strong first half and it was exactly our gameplan. I think we managed the game very well and created a lot of situations. We controlled the game and the threat of Jamal Lowe. Just before half-time we conceded a goal which was really a pity but I told the guys to stay in the game and be more clinical.
"The second goal was stupid, a bad decision and a mistake that was easy to avoid. We have showed we have the mentality to stay in games and come back from 1-0 but that goal killed the game and our performance."
The opener saw Ben Cabango, one of two players left to be marked by Michael Sollbauer, head in a long throw-in. Ismael said: "The throw-in was very good, four players jumped for it, it could be our guys but it was their guy who won it. It was a 50/50 situation. I am more frustrated about the second goal."
It was 2-0 when Mads Andersen headed the ball into Michal Helik and the ball rolled to Lowe who had been in an offside position but was put clean through to score.
Ismael said: "It was offside and also we could have had a penalty (for a handball late on) but we made the mistake. We have to clear the ball, it's not about offside. The failure is on us. This mistake was completely stupid."
Barnsley have lost their last two league matches against the top two sides in the Championship Norwich City and Swansea. Ismael said: "They are the best two teams but the two games were not so clear. I can lose but the opponent has to be better than us and I can say 'OK, congratulations' and move onto the next game. But that was not the case tonight. We made some gifts to the opponent to win the game. It is good that we can compete with the best teams in the division but we have to stop these mistakes."
Callum Brittain added: "We were really good in both halves. There were parts of the games that could have been better. The first goal was a lottery goal. Five players have gone to head it and it's come off his head and gone in.
"Then there was a silly mistake for the second goal. I think we were the better side against the team that is second in the league for the majority of the game."
On the error by Andersen and Helik, Brittain said: "Anyone would be disappointed if they made a mistake that led to a goal. But it's football, these things happen. The rest of us will get around them and get their heads up. They are two good players who are both playing well at the moment. They can't think about it too much."