Steve Evans will be taking his team to confession after a "cardinal sin" cost them all three points at Grimsby Town.
Jake Reeve's 79th-minute goal had put Boro in front at Blundell Park and despite late pressure, they looked to set for another away success.
But a shout from goalkeeper Taye Ashby-Hammond stopped them from clearing a corner in the first minute of stoppage time and Niall Maher poked home an equaliser for a 1-1 draw.
The Stevenage boss was visibly fuming at the final whistle but felt the game should have been wrapped up long before the final act.
He said: "For the first 25 minutes we were camped in their box and we miss the best chance of the season to go 1-0 up.
"They counter attack from a poor set play from us and get a penalty.
"He’s dived, there you are, he’s just dived.
"Taye comes out and from the referee’s point of view, he thinks there is going to be contact when you go over like that.
"But justice was done and we controlled the second half.
"They were always going to counter attack, that’s how they play.
"We changed the shape of the team, we had to with [Danny Rose] coming off, and it worked.
"The two players we introduced, David Amoo and Jamie Reid did great and we got a great finish.
"But you have to see it out and if you make a huge error, a cardinal sin in Catholic language, you get punished.
"It will be a long, disappointing trip but we understand why they have got back into the game.
"It doesn’t matter if you are playing Grimsby or the Red Lion, if you make a big error, and this was a big error, you get punished."
While the error irked him greatly, the fact they never converted pressure into chances and goals was also a huge bugbear for the Boro boss.
"After we score we make an incredible chance and [Luke Norris] should score," he said.
"If he takes it with his other foot he probably does.
"He’s run himself into the ground and I thought our shape was good. They didn’t have a clue where we were.
"That was typified in the first 30 minutes where we were totally dominant.
"We’ve not played that shape very often but it worked really well.
"This is a tough place to come and this was possibly our best away performance in a while.
"But we should be in a commanding position and two or three ahead after 30 minutes.
"I can’t explain how we missed that chance early doors but we miss it."
The lead-up to the goal came with the double substitution, acted on when Danny Rose took a knock to the back of the head.
"He got a bang," said Evans, "and strikers get bangs every game but we are a safety-first management and medical team so we [took him off] as a precaution.
"We’d actually contemplated taking him off anyway.
"Luke Norris was outstanding for us last season playing up front with two wide players and David Amoo gave us a spark every time he got the ball, every time he got it he created havoc.
"We didn’t give it to him in good areas enough but we’re finally seeing the David Amoo we signed in the summer.
"We changed it positively to win the game and that should have been enough to win the game."
The lesser-seen starting formation changed by the substitutions featured a back four and Max Clark pushed into midfield.
Evans was pleased with how his wing-back performed further forward.
He said: "He’s played a lot of games there in League One and the Championship, he’s very competent there.
"We played him there in a pre-season game in a closed-door game against a strong West Ham side and he was outstanding.
"We also recognised the strengths of Grimsby in wide areas and there were one or two little problems but if we look at it over the piece and if we see it through, everyone is saying what a brilliant away performance.
"But it’s not a brilliant away performance because we haven’t won."
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