Inter coach Jose Mourinho admitted his side were "terrible" in Sunday's 3-1 defeat at Atalanta and accused them of conceding goals in a "ridiculous manner".
The Nerazzurri found themselves 3-0 down inside 33 minutes in Bergamo with their sole response coming late on through Sweden striker Zlatan Ibrahimovic.
The defeat saw Inter's lead at the top cut to three points over Juventus at the halfway stage of the Serie A season.
"Our approach was completely wrong and I don't know why," said Mourinho. "We didn't have the right mentality going into the game.
"This game was our worst of the entire season. Against Atalanta, my team were terrible."
Sergio Floccari gave Atalanta an 18th-minute lead before two goals in 15 minutes from Cristiano Doni all but settled the outcome and gave the hosts their first win over Inter in almost 15 years.
"I cannot comment on my team's performance in the opening 30 minutes," said Mourinho.
"They (Atalanta) took four shots on goal and scored three times, but those goals we gave away in a ridiculous manner.
"You end up paying for mistakes."
Mourinho, whose side have lost just twice in Serie A this season, admitted he and his players deserved all the criticism directed at them.
"As coach I take full responsibility," he added. "I need to be silent and all of the sporting press can use any type of adjective they want to describe our performance and I will accept it.
"We have to accept all the criticism."
Inter have been sluggish since the resumption of Serie A following the Christmas break.
They opened with a 1-1 draw against Cagliari before yesterday's capitulation.
But Mourinho defended their record overall and insisted the other teams in the top flight would happily swap positions with the league leaders.
"I can only say that 19 teams would be very happy to be in the position that Inter are in," said Mourinho.
Inter host Sampdoria this weekend while Juve entertain Fiorentina. AC Milan, six points adrift, travel to Bologna.
Source: Sporting Life