Maurizio Sarri admits Tottenham destroyed his Chelsea players when they handed them their first defeat of the season.
The two clubs face each other in the first leg of their EFL Cup semi-final on Tuesday night with Spurs holding a huge psychological advantage because of what happened just over six weeks ago.
Sarri's men arrived at Wembley in late November boasting an unbeaten record in all competitions, but were totally outclassed in a 3-1 loss.
Chelsea have gone on to lose twice more since then and have struggled for form - a win over Manchester City aside - ever since.
Sarri reveals Spurs' performance stunned his squad and made him fully understand the fierce rivalry between the two clubs.
He said: "I saw my players in the dressing room after the match. They were destroyed.
"I realised that the match against Tottenham is a very important match for the club, the fans and the players as well.
"What did I say to them? They needed only to realise why the match was so bad and it was really very easy because the video of the first 15 minutes was clear.
"There was a big difference in mentality, aggressiveness and determination so it was clear. Clear for me and also for the players."
Chelsea have already had to beat Premier League leaders Liverpool to get this far and are extremely likely to meet Man City in the final if they get past Spurs, because Pep Guardiola's men face League One outfit Burton Albion in the other semi being played over two legs.
The trio make up the top three in the top flight and Sarri believes winning the competition is proving as tough as the Champions League.
In Pictures | Tottenham vs Chelsea | 24/11/2018
He added: "Here everything is really very difficult. If you think in the League Cup we played against Liverpool, now we have to play Tottenham and then probably against Manchester City in the final.
"It is like to play in the Champions League I think because the League Cup is really, really very difficult. The level of opponent is a really high level.
