Antonio Conte called on Chelsea to rediscover the Premier League winning characteristics of last season after a chastening loss at Roma.
The Blues were beaten 3-0 after a "really bad" second half performance, but the damage was done as early as the opening minute.
Stephan El Shaarawy scored after 38 seconds, then pounced on an Antonio Rudiger error to make it 2-0 after 36 minutes before Diego Perotti struck a fine third in the second half to take Roma above the Blues in Champions League Group C.
A win in Conte's first match in Italy as Blues boss would have seen Chelsea advance to the knockout stages, but instead he was left to ponder how to respond on Sunday against Jose Mourinho's Manchester United.
"Last season we showed great hunger, great will to do something of importance. Last season we won the league and did a miracle," Conte said.
"If we think that only because our name is Chelsea and the opponent has fear for the name Chelsea, I think this is not the right way.
"We must find the hunger that we showed in all games last season and in this season sometimes.
"This season we have to dig very deep if we want to be competitive and fight for something important. If we are not ready to dig deeper, we can have this type of game."
Chelsea looked to be coasting in Group C after following up their opening 6-0 win over Qarabag with victory at Atletico Madrid.
But after conceding six goals in two games with Roma, the Blues need points in Azerbaijan before the final group clash with Atletico.
Conte insisted he was content with Chelsea's first half performance, but not the second.
"What I'm most disappointed about was the performance in the second half when Roma had more hunger, more desire, more fight to beat us and clearly deserved this win," he said.
"The second half was really bad, bad for a team like us. I didn't see positive things."
Roma boss Eusebio Di Francesco, meanwhile, was overjoyed by his team's performance.
"We really deserved this," Di Francesco said.
"Our fans deserved this great win, and it's no coincidence I played many players today who helped get us into this competition.
"We have gained self-belief. There are more fights to come to establish ourselves, but we've proved we can play against any team with this mindset and collective effort."
