There was a fight here if Diego Costa had wanted it. First, Damien Delaney whacked him painfully through the back of the calves. Later, Scott Dann aimed a frustrated hack at the Chelsea forward, scything him down with the ball metres away.

On another day, perhaps Costa would have invited both (Crystal Palace) centre-backs to join him for a full and frank chat in the tunnel. But here (at Selhurst Park), in the downpour, he did a strange thing. He picked himself up and got on with the game.

Something seemed to have changed in the Chelsea forward's mind, a switch flicked, a different setting. "We try to get him to focus on what he's good at but not wasting energy on tonterias (Spanish word for 'silly things'), to show what he is able," explained Chelsea manager Guus Hiddink.

It sounds so simple. It is one of those transformations that can easily be ascribed to a change of manager. It fits an appealing narrative, and there is no doubt that Jose Mourinho's departure has released an almost intolerable pressure within the Chelsea dressing room.

Now that Mourinho has left, Costa is looking back to his old self (making an assist for Chelsea's opening goal and adding their third with a tap-in), playing like he was here to concentrate on his football, not audition for a Spaghetti Western as the baddest gunslinger in town.

Would he have returned to form whoever was in charge? Probably. Has the introduction of a new coaching voice - rather than Mourinho picking fights, adding intensity and pressure - given him a lift, a little boost of confidence? Almost certainly.

Perhaps all we can judge for certain is that, after surviving 20 minutes of pressing from Crystal Palace, Chelsea played with a lack of inhibition that did nothing to dispel the notion that Mourinho's exit has eased the tension.

We can ask what it says of the players, and their dedication, when such a talented group can slump so low - but, equally, what will it say of Mourinho if this revival under Hiddink does turn into a charge up the table, perhaps even a run in the Champions League knockout rounds?

(Former Arsenal player and manager) George Graham used to advise new managers to walk into the dressing room, look around at the players and remember: "These are the b*****ds who cost the last guy his job."

But if those b*****ds start to play like they are happy again in their football - as Cesc Fabregas, Oscar, Costa and the recently restored John Obi Mikel certainly did in victory (on Sunday) - then it reveals something pretty fundamental about how Mourinho's powers of motivation among this group had waned.

It would be rash suddenly to hail Mikel as the missing piece of Chelsea's midfield when he has never fully exhibited that reliability over almost a decade.

But his recall, and the pressure it has put on Nemanja Matic to raise his game, indicates that Mourinho's over-reliance on a small core of players could have been self-defeating.

Even with Eden Hazard limping away after 19 minutes, Chelsea easily had the better of them (Palace) and a pattern of one win - and only one win - per month in the league this season should now be ended, given West Bromwich Albion and Everton are soon up at Stamford Bridge.

The mood is transformed, with Chelsea players applauding the travelling fans at the final whistle. Not so long ago Costa was being jeered off the pitch.

If Chelsea, and their main striker, can keep avoiding tonterias, they may yet finish in the top six.

THE TIMES, LONDON