Chelsea Must Hope Diego Costa's Porto Display Is Not Another False Dawn.

 In the final minutes on Wednesday, the Chelsea fans chanted Jose Mourinho’s name. The manager has largely retained the faith of Stamford Bridge, but it must still have been a welcome sound after the boos that greeted the final whistle after Saturday’s 1-0 home defeat to Bournemouth.

 The performance too must have come as a relief. This was by some way Chelsea’s best display of the season, even if certain doubts remain—most notably over the form of Diego Costa.

  The fans also chanted Costa’s name at various points—most notably on the two occasions when he got opponents booked. They have clearly not run out of patience with the 27-year-old despite his indifferent form this season, and there were perhaps signs that he, like Chelsea, is beginning to turn his season around.

 He is still, though, a player desperately short of confidence. “It’s clear, but I think what was also clear was his effort, his commitment [and] his great movement, which is something he hasn’t had for a couple of months," Mourinho agreed. "I think his movement was great.”

 Up to a point, there was self-congratulation in the observation after the news Mourinho has spent the past few days working with Costa, reminding him of the fundamentals of forward play. But however it was achieved, Costa was better here than he has been for some time; Mourinho deserves some of the credit for the attacker's improvement.

 The assumption all season has been that at some point Chelsea would turn the corner. There was some thought they’d done it when they followed up a victory over Aston Villa with a draw away to Dynamo Kiev and more concrete signs of recovery when they beat Norwich City and Maccabi Tel Aviv then drew at Tottenham Hotspur.

The defeat to Bournemouth seemed to have punctured that bubble, but it may be it comes to be seen as a blip on the road to something approximating to the standards expected of champions.

 Mourinho’s pre-match press-conference had been an oddity as he reeled off the sort of statistics he has in the past disregarded—even getting one of them, chances created, badly wrong. It was a performance that seemed worryingly similar to Rafa Benitez’s notorious “facts” rant in 2009, but perhaps there was some substance as he outlined all the ways in which Chelsea have improved.

 Porto were surprisingly supine—perhaps playing Chelsea’s reputation rather than the actuality this season—but it was still impressive how comfortably Chelsea held off a side that had suffered only one defeat all season. Perhaps it would have been different had Chelsea not had the good fortune to take the lead through an own goal after 12 minutes, but they did.

 As Mourinho noted, that settled Chelsea and meant Porto had to score at least twice. Yacine Brahimi caused occasional problems, and while there was a sense one goal might have reawakened Chelsea’s neuroses, it never came. Willian was as diligent and reliable as he has been all season, Kurt Zouma excelled and Nemanja Matic offered signs he is beginning to emerge from his slump.

 But it was Costa's variable form that most caught the eye. In the build up to the first goal, there was a flicker of the Costa of old. He bullied his way onto Eden Hazard’s through ball but then, with time and space, hit his shot straight at Iker Casillas in the Porto goal, the ball bouncing back to hit Ivan Marcano and go in.

 As a one-off incident, it would be harsh to blame the centre-forward for the miss, but it was not a one-off and, as Mourinho noted while praising his movement, “last season he would score immediately." That spell before Christmas last season when it was taking him under four shots per goal seems a long time ago.

Twice in the second half he was set clean through behind Porto’s defensive line. The first time he hesitated, perhaps slightly miscontrolling, and then, as he checked inside—something only made necessary by the hesitation—he was muscled off the ball by Danilo Pereira. “You could immediately feel the lack of confidence because the first thing he did was not attack the goal but look to the linesman,” Mourinho said. “When he did that he lost an important second.”

 Eight minutes later, he was let down by his second touch, which was almost inconceivably heavy. He is still a player ill at ease with himself and his surroundings. “His last touch on the ball was not the best,” Mourinho said. “He could have scored two or three goals. There is a lack of confidence, clearly, but his attitude was very good and his movement was much better, so goals are coming.”

 That is what he believes about his side as a whole, and perhaps he is right. This felt like the most, for want of a better word, normal game at Chelsea all season. At the start of the second half, there was a thought the Chelsea of old would finish this off but the Chelsea of this season might succumb to nerves, but Willian’s goal seven minutes in put paid to the latter.

  Costa played a key part in that, taking an awkward ball down well before laying it off to Hazard to set up Willian. That showed a quality of touch that has been lacking all season. But the other side of his game, the preference for brawling over playing, which has seemed almost a fallback as lack of self-belief has impaired his technical qualities, was also evident.

  In the first half, with chelsea leading and seemingly comfortable, he needlessly got involved in an altercation with Casillas after treading on his foot. Perhaps it was an accident, but Costa is unusually careless where other people’s feet are concerned. It didn’t even make sense in pragmatic terms;

 Chelsea were in control, so what was the utility in breaking that rhythm and possibly riling Porto into action? As it was, he merely induced two opponents into getting booked for fouls on him before half-time.

 That side of his game has always been there—it’s just become ore pronounced as the goals have fallen away. It’s an annoyance and an irritation, for those watching as well as those playing against him, but at last there were some positives to go alongside it. Costa isn’t back yet, but he’s closer than he’s been for months—and so too, perhaps, are Chelsea.