It's going to take Diego Costa more than a few kisses and cuddles

To anyone else, a 4-0 away win in the Champions League would be met with yelps of satisfaction and cup-runneth-over delight. But this is Chelsea. In this season.

Inevitably, then, the verdict of this result over Macabi Tel Aviv - which, on a comparable basis, was only one goal shy of Barcelona's 6-1 thumping of Roma on the same night - was branded by the press this morning as "unconvincing". A tad unfair? Well, maybe, but not a lot.

Former Chelsea defender Tal Ben Haim's sending off before half time, for a ludicrous kick at Diego Costa, should have tipped the balance in the Blues' favour, especially with them up 1-0 after Gary Cahill's 20th minute goal. But as so often is the case, losing a man can galvanise a team, and as happened with Stoke City, Tel Aviv came out of the traps in the second half.

It wasn't until the 72nd minute - and another superb Willian goal struck from a free kick - that Chelsea were able to make the game safe. This spoke further volumes about Chelsea's enduring inability to kill off games against stubborn opponents.

That strikes from Oscar and Zouma followed in the following 15 minutes were, perhaps, not a surprise, given that Tel Aviv were tiring with a man less and growing increasingly ill-disciplined. But the weaknesses that have plagued Chelsea since the start of the season were still there, despite José Mourinho's maintenance that confidence is returning to the side.

In fairness, overall it wasn't a bad performance by Chelsea, and a welcome back-to-back win after their result on Saturday over Norwich. In Hazard and Fabregas, something of their best is returning. But whatever improvements are in store throughout the team must still be to come. The defence still looks stretched at times - Peretz was a regular terror last night - with Terry and Cahill still straining more sinews than you would have expected were needed to keep danger away from the impressive Begovic in goal.

However, the area of greatest concern remains in front of the opposition goal. Apart from one thwarted bicycle kick that was almost on target, Diego Costa is still frustratingly profligate. A lack of confidence may seem an odd diagnosis for a player so seemingly ready for a scrap that he makes Dennis Wise look like Henry Kissinger. But what energy he has, he seems to channel all-too easily into niggly flair-ups that detract from his striking prowess.

It's a frustration that is shared by Mourinho, who was clearly agitated in the technical area during the first half with Costa apparently not following orders. For the rest of us watching, it is Costa's lack of real movement off the ball and positioning to slam passes into the net that is the most frustrating.

Something has ailed Costa all season. Despite discounting summer rumours that he was homesick in London, and then confessing that he'd returned from the summer break overweight due to a little too much home cooking in Brazil, there has been a discernable air of ill-ease around him since the start of the season.

Whether he is overthinking everything, or not thinking at all, Costa is still a problem for Mourinho, and in turn that creates other headaches, seeing as Falcao is out injured (and wasn't doing much beforehand, to be honest), and Loïc Remy is still not regarded as the first-choice target man.

"I was disappointed. I reacted and he reacted too," Mourinho said of Costa in the first half. "At half-time in the dressing room there were a few kisses and a few cuddles." Well I'm sure some TLC was appreciated by the Brazilian, but that still doesn't fix the underlying problem.

Costa can't be blamed for carrying all of Chelsea's weaknesses this season but he is obviously toiling. The solution, isn't, either, to buy in the January window. The Torres saga, not to mention the shotgun purchases of Mohammed Saleh and Juan Cuadrado, should warn them off that route.

It goes without saying that any striker worth their salt will not be on sale in the middle of the season. Which means that, unless Lionel Messi decides that London is where he wants to be for the second half of 2015-16, Mourinho needs to make use of what he's got. Specifically, Diego da Silva Costa. Because there won't be anything new coming along until next summer.