IF Middlesbrough do end up missing out on an automatic place by a couple of points come the end of the season, or even worse a Championship play-off place, then supporters are unlikely to forget the afternoon when it all went wrong against Brentford.

Against a team, albeit a talented one, which had only won once away from home, Boro let three points slip away and there were a raft of reasons for it.

Only one, though, is likely to be remembered by supporters this morning: Tony Pulis’ decision to replace a top scorer with a full-back with under half an hour remaining when Middlesbrough led by a goal.

There were arguments to justify the decision. Britt Assombalonga, the forward who made way, was not playing as well as he has been; George Friend, the man who came on, should have strengthened a left-side that had been tormented by the Bees; and the switch allowed greater freedom for Jonny Howson down the right.

But what Pulis clearly hadn’t taken into account was the reaction of the home support when he made a move that smacked of negativity. Despite leading, the fans let their feelings known instantly by greeting the substitution with boos and gave Assombalonga a standing ovation.

The atmosphere had turned, more nerves were instantly apparent within the way Middlesbrough played, and within eight minutes Ashley Fletcher’s sixth minute opener was cancelled out when Ryan Shotton turned Henrik Dalsgaard’s low drive into his own net.

There were sarcastic chants of “Britt Assombalonga” from the stands and those had only just died down when Dalsgaard teed up the tricky Said Benrahama to hammer Brentford in front.

It didn’t help that both goals arrived down Friend’s side, even though he was not necessarily to blame for either, and then a section of the South Stand directed “you don’t know what you’re doing” in the direction of Pulis.

There was a hint of admission when he reflected that “it wasn’t a popular decision” and “if I made a mistake, I made a mistake, and I will hold my hands up.”

Pulis then went into the media suite and explained: “Jonny was getting pulled back first half and I thought if we changed that it would give Jonny more room to get forward on the other side which is where I thought we were getting most joy.

“That gave Shotts a bigger area to look after on that side but it also gave Jonny the opportunity to get up and around where he wants to be. In the first half he was getting pushed back and doing most of his work in and around the back four.

“Obviously you take stick when I took Britt off and I accept that as a manager. I took him off because I thought it was right to take him off and you have to stand by your decisions.If Britt was smashing it in the back of the net and doing stuff then fine, but I thought he looked a little bit flat.”

Assombalonga certainly wasn’t happy either, and he let his feelings known when he trudged disconsolately towards the dug-out after being replaced by Friend.

The truth is, he wasn’t actually playing that well but it would be ignorant to suggest the change didn’t have an impact on the remaining minutes of the game because the atmosphere certainly deteriorated.

Pulis was angrier with referee Jeremy Simpson and his officials, believing Middlesbrough would still have won that game – or at least claimed a point – had big decisions gone the Teessiders’ way.

And when Middlesbrough led, courtesy of Fletcher’s second in as many home dates after reacting first to poke in a Mo Besic strike that was spilled by goalkeeper Daniel Bentley, they had other opportunities.

Fletcher’s moments before Assombalonga’s withdrawal was the pick, when he directed a header at the back post wide from Shotton’s delivery when his strike partner looked as if he might have stuck out a leg to turn over the line too.

Pulis said: “I’ve looked at the videos and – I haven’t seen the referee – the Saville one (foul) first half, Jonny isn’t a diver yet he got booked and looking back at it (on video) the lad catches him.

“Dani Ayala from the long throw, again the referee’s got a great view of it and the lad just pulls him down. He has his hands around both sides of his head and he just pulls him away from the ball.

“They’ve got to be getting those decisions right. I do accept that there are times in the game where the referee will have somebody in the way or it’s one those decisions where you are too far away to call it.”

Simpson made inconsistent decisions all afternoon, which didn’t help the flow of the game. Middlesbrough should have managed to see the victory through after claiming the early advantage.

The danger signs had already been there. Sergi Canos was particularly threatening and had a goal ruled out for an apparent trip on Saville by Neil Maupay, rattled the crossbar and forced Darren Randolph into the brilliant one-handed save. Maupay had also headed in and had that ruled out for offside.

But Brentford got their reward when Saville’s tame attempt at a clearance resulted in Dalsgaard managing to force Shotton into finding his own net, and then Dalsgaard got in behind to create the opening for Benraham.

Pulis, whose side are now 12 points off second spot and only four clear of seventh, said: “We make two mistakes, two terrible mistakes that we haven’t done all season.

“Shotts could really leave the ball. It’s difficult, I understand that, but he could have left it and it would have gone out. And the second one the two Georges get mixed up.”