Unai Emery rued missed chances after Aston Villa were defeated in the FA Cup third round by Stevenage.
Morgan Sanson’s first-half opener looked to be enough to see the hosts through against their League Two opponents.
However, late drama saw Boro score twice in the final few minutes to knock Villa out.
Emery said: “The big mistakes were in 90 minutes because we had the chances and we didn’t score.
“So many chances, getting into the box, and we were not clinical enough to score the second goal and finish the match.
“At the end, they really played with the possibility in their mind to make us make a mistake. They played with long balls, second actions and crosses, and they pushed for a draw.
“We didn’t control the match in the last few minutes, thinking ‘Ok, we are going to play the next match against them’.
“We can only make one mistake, not two.”
Defeat was the club’s eighth consecutive loss in the competition, dating back to 2016.
Emery was disappointed to have exited the FA Cup but said he will pick the players up quickly as the focus returns to Premier League action on Friday night.
“We are so sorry for the supporters – I’m very upset, like them,” he said.
“Now it’s my idea to try and come back so quickly thinking about the match here at home on Friday against Leeds United.
“We can speak about the match we played today and the FA Cup and how it was very important for us to do something we haven’t done for a long time.
“My process here started two months ago and to feel this way is a process too – not a good process, being disappointed, but we are going to work to try and identify the things we have to improve.”
