The hosts took the lead early on but then conceded three goals as they slumped to a third straight loss.
Head coach Stendel told the Chronicle: “It is hard to accept the performance today. We started well and took the lead, and the performance in the first 15 or 20 minutes was everything we wanted. In the first half half, I cannot say we played bad but Brentford played so much better after 20 or 25 minutes.
“They found easy ways to break our press and scored goals that are too easy for the Championship. In the second half, Brentford were better again and we couldn’t cope with their game. It was hard to watch for the last 20 minutes for us, for the supporters and for the players.
“Brentford is a better team than their place in the table, they didn’t show it in the last games but they showed it today. We only played as well as we have in the previous games, like the second half in Nottingham Forest, for the first 20 minutes then after that we were not good enough."
Stendel said he could understand the supporters' frustration after a third straight home loss. He said: "When I am a fan and I watch this game today, I am not happy. I told the players at half-time that when the stadium is quiet, it is not good. The players gave the supporters a good feeling in the first 20 minutes but it was so quiet before half-time that I could call over the pitch and they hear me. We need to give the supporters the feeling that we are one unit, we didn’t do that in the second half."
The Bees’ front three of hat-trick hero Ollie Watkins, Sergi Canos and Said Benrahma caused major problems for the home defence. He said: “We could not defend them but they also have a lot of quality. They were given the space they needed to show their quality. We tried to change in the second half but, in the first minute, they scored and that was the knockout for us.”
Barnsley are now three points adrift of safety in 22nd having picked up five points from nine games, without a win in eight. Stendel said: “We are all disappointed but I can only say we will work very hard. We are working as hard as last season but we need to accept this is a different league with different quality. We need to be realistic about the quality in our team. At the moment, we are not getting the right results but the good thing is we have another game on Wednesday (at home to Derby County).”
Cauley Woodrow put the Reds ahead with a superb long-range strike in the first minute. Stendel said: “We spoke to Cauley about his performance and his game. He has a lot of experience in the Championship and we think he has the quality to score more than one goal by this point in the season. He had the right reaction today but, after three games without a goal, we scored then conceded three. It is hard to accept it.”
Midfielders Mike Bahre and Cameron McGeehan missed the game through injury and illness respectively. Stendel said: “Mike Bahre was ill last week. He trained on Friday but you could see he didn’t have the power to play. Cam McGeehan had an injury on Wednesday. He will not play this week. It is a muscle injury and he cannot train. I don’t believe he will play on Wednesday.”