Antonio Conte felt Roma showed greater desire as they sank Chelsea 3-0 and he urged the Premier League champions to pull together before Sunday's showdown with Manchester United.
Chelsea ceded top spot in Champions League Group C after Eusebio Di Francesco's side stormed to a convincing triumph at the Stadio Olimpico, Diego Perotti firing home a superb third after Stephan El Shaarawy hit a first-half brace.
Head coach Conte has prickly deflected questions regarding his future over recent weeks and accepted his side failed to measure up in the Italian capital.
"When you concede three goals you must be worried because it means something doesn't work," he told BT Sport.
"It's very difficult now to tell [what this is] but for sure we have to analyse the game. I think we needed to work on the tactical aspect.
"For sure, in this season, we are working less on this aspect and we are paying in this situation.
"I think we have to look at ourselves, our performance and to understand that tonight was a bad night for us.
"I hope, just one night, I hope. I work, I put [pressure] on myself to have only one night like this.
"We must work together and have this will together."
El Shaarawy fired in a spectacular opener after just 39 seconds and the former AC Milan youngster doubled the advantage thanks to a woeful error from ex-Roma man Antonio Rudiger.
In between those goals, Chelsea enjoyed their best spell of the match but were overwhelmed after the break and fortunate not to suffer more damage.
"I actually believe we played a good match in the first half, but were 2-0 down," Conte said at his post-match news conference.
"We could have scored after 30 seconds and then suffered on the break. We created many chances, were not clinical and ruthless enough, then suffered from their second shot on target.
"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.
"We lacked everything in the second half and Roma were the better team in every point, in terms of motivation and hunger."
He added: "For sure, we have to try to find the strength to understand and to use this loss in the right way. Because, as I said before, 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."