Mauricio Pochettino admitted Chelsea's 1-0 defeat to Aston Villa in September had a "big impact" on his players' confidence.
Ollie Watkins' second-half winner saw Villa claim all three points at the Blues' expense after Malo Gusto was shown a straight red card for a challenge on Lucas Digne.
The two sides meet again in the FA Cup fourth round on Friday night and Pochettino believes the manner of the defeat stunted his young Chelsea side's development.
"The way we lost the game against Aston Villa was a big impact because I think we deserved (to win) with 10 men," Pochettino told a press conference ahead of the fourth-round clash at Stamford Bridge.
"We were pressing high, we created two big chances and we didn't score and we conceded in a chance that was unbelievable because we were the only team trying to score and press.
"That was a massive impact in our confidence. If we scored and won the game with 10 men against a team like Aston Villa it should be a big boost for us, massive in confidence and belief and (give us) the capacity to grow quickly.
"This type of result sometimes delayed a little bit the capacity to grow and if you win the game it's like everything starts to run much better."
High-flyers Villa sit five points off Premier League leaders Liverpool in fourth and advancing in the FA Cup would only strengthen an already memorable season.
Pochettino insisted the difference between his ninth-place Chelsea and Unai Emery's side has nothing to do with the quality of squad, but instead confidence.
The Argentinian manager suggested that if Chelsea had beaten Villa in September then the result would have galvanised his players to be in a better position.
When asked if Villa have a stronger squad than Chelsea, Pochettino added: "No. This moment is confidence.
"If rather than losing the game with 10 men and we won the game, it would be the opposite position than we are now, maybe, I don't know.
"The reality is our reality. We did not compete in the way that we should for many details, we are talking about details with the squad, the players, meetings, in training."
Armando Broja has been linked with a move away from Stamford Bridge this month but his manager highlighted the Albania international's potential, insisting the 22-year-old needs time to develop.
Pochettino said: "The potential is massive. Of course, it is about a process.
"All the biggest strikers always need time. When they are young, they need to find their own balance. But I still believe that he has the potential to be an amazing striker."
