ROME -- Antonio Conte said there was cause for concern, and warned his Chelsea players that they cannot hope to compete for trophies this season unless they rediscover their "hunger" after the Premier League champions were humbled 3-0 by Roma.

Two goals in the first 36 minutes from Stephan El Shaarawy put the home side in control but it was Chelsea's second-half display that angered Conte, as Diego Perotti's long-range strike put Roma out of sight and condemned the Blues to a first defeat in this season's Champions League group stage.

Atletico Madrid's failure to beat Qarabag means Chelsea are still well positioned to qualify from Group C, but Conte was in no mood to dwell on the positives.

"When you lose 3-0, it means it wasn't a good performance. Our first half was good, we created many chances to score, but to be 2-0 down was unfair," Conte told BT Sport.

"But in the second half, it was a really bad performance. Roma showed more will to fight and more desire to win the game. I'm very disappointed with our second half. For this performance, we all have to take responsibility.

"When you concede three goals, you must be worried. It means something doesn't work. It's very difficult now, but we have to analyse the game. We need to work on the tactical aspect. We are working less on this aspect this season. We have to look at ourselves.

"Tonight was a bad night for us. I only want one night like this and we must work together this week."

In his news conference, Conte expanded on lamenting in his side's desire compared to Roma's.

"What I'm most disappointed about was the performance in the second half," he said. "Roma had more hunger, more desire, more fight to beat us and clearly deserved this win.

"We have to try to find the strength to understand and to use this loss in the right way. In this season we have to dig very deep, very deep, if we want to be competitive and to fight for something important. If we are not ready to dig deep, we can have this type of game.

"We have to know this. Because, I repeat, this season will be very difficult if we don't understand quickly the right way that we have to go."

Stephan El Shaarawy scored in the opening minute as Roma ran over Chelsea. Shaun Botterill/Getty Images

Chelsea's performance is particularly concerning for Conte with Manchester United due to visit Stamford Bridge on Sunday. To compound his worries, N'Golo Kante indicated after the game that he is not yet sure whether he will be fit enough to return, having been omitted from the match day squad against Roma.

"My task is to try to find the best solution," Conte added. "To try to avoid this type of game. But, for sure, we have to work together. We need to have the will -- I repeat -- to dig deep. If we think that only because our name is Chelsea, and the opponent have fear of the name Chelsea, this is not the right way.

"We have to find the hunger we showed all last season and, this season, only sometimes. But this season has been up and down. If you are a great team you must have stability. You must have consistency. At this moment we are struggling a lot to find this type of balance.

"Last season we showed great hunger, great will to do something important. We won the league and did a miracle. But if we want to be competitive this season we have to avoid these ups and downs. A great team must have stability and great desire to be protagonists in every game."

Goalkeeper Thibaut Courtois, beaten six times in two matches against the Serie A side, urged his teammates to respond positively against United.

"We felt good at half-time because we played well, but I don't know why in the second half we dropped our fighting spirit and our mentality," he told BT. "We have to fight back on Sunday and show the fans this was an off day.

"It's hard to say what the problem is. Last season, there were games where I had nothing to do and other games I had four or five saves.

"This season every game is a hard game and we have to find the mentality of clean sheets and not conceding goals."