Manchester City manager Roberto Mancini suggested Chelsea defender Ashley Cole was at the centre of a tunnel bust-up following the Londoners' 2-1 win at Stamford Bridge.
Although it seemed reasonably peaceful after the final whistle - Andre Villas-Boas and Mario Balotelli exchanged a friendly greeting - there was some underlying tension at the manner of Chelsea's victory.
And Mancini claimed some pushing and shoving had been triggered by Cole, something later denied by Villas-Boas.
When asked what had happened, Mancini said: "I don't know if Cole said something.
"I don't know what he said. I don't understand."
Of more concern to the City boss were a succession of decisions he felt had gone against his side, leading to their first Barclays Premier League defeat of the season.
Balotelli put the visitors in front after less than two minutes.
However, referee Mark Clattenburg missed what appeared to be a clear foul in the penalty area on David Silva by Jose Bosingwa.
He then sent off Gael Clichy - City's third red card in six Premier League games - before awarding the home side a spot-kick eight minutes from time when Daniel Sturridge's piledriver struck Joleon Lescott on the arm.
"I agree with all of his decisions," said Mancini, with more than a hint of sarcasm.
"There was a big penalty. There wasn't a fan inside the stadium who didn't see it.
"But the referee was very close and he didn't.
"I don't know (about Chelsea's penalty).
"The Chelsea player shot very hard from five or six metres. It is difficult for the defender.
"But, at that moment, the referee was really sure.
"It was after the sending-off, that the game totally changed."
The result leaves City just two points clear of Manchester United, who will leapfrog their neighbours if they win at QPR on Sunday lunchtime, four hours before the Blues entertain Arsenal.
"It doesn't change anything for us, because we knew before this we should lose a game at some point," said Mancini.
"It is unusual that a team comes to Chelsea and plays like we did in the first half because we dominated the game.
"We didn't deserve to lose but we did.
"The season is very long and very hard. Now we should prepare for another difficult game, against Arsenal."
Meanwhile, Mancini confirmed he will take no action against Balotelli for breaking a 48-hour pre-game curfew by going for a curry in Manchester on Saturday night.