Pairing up: why Chelsea's two-man left flank adds up to less

What happens when a side that cannot stop winning fields a partnership that cannot stop drawing?

Chelsea's season reads like a misprint. Thirteen league games unbeaten, thirty-seven points on the board, a five-goal dismantling of Everton among the evidence, and the champions setting a pace nobody in the English Premier Division has matched. Slice the campaign by personnel, though, and a strange shape appears.

With José Calderón and Lionel Messi both on the left flank, Chelsea have played eight games: five wins, one draw, two defeats. That is 2.5 goals scored a game and 0.6 conceded. Without one of them — twenty-five games — it is twenty-one wins, two draws, two defeats, 3.0 scored and 0.6 conceded. The defence, to its credit, does not care who is on the pitch. The attack does.

Half a goal a game is not a rounding error. Across a season it is the difference between a title canter and a title race, and it turns a side that wins three games in four into one that wins five in eight. The partnership is not broken; it is simply outscored by the alternative.

Calderón arrived from Oviedo on 12 January this year for £103.4m, and the fee framed him as an addition rather than an experiment. Forty games and two goals into his Chelsea career, he is a left-back whose value shows up in the scoreline rather than the scoresheet. Messi, who came from Club Atlético Boca Juniors on 20 June 2059 for £6.2m, has 86 goals in 217 games for the club and 21 in 42 for Argentina — a scorer's record that makes the dip beside Calderón harder to explain away.

"We keep looking at the same clips," a figure close to the dressing room said this week, which is the sort of thing people say when the clips have stopped being the problem.

Context matters. Chelsea's unbeaten league run has been the talk of England, and the fixture list has not been kind: a Champions League trip to Graz, an Arsenal side arriving with the chances to trouble anyone, a derby against West Ham in which Maurício came back to haunt his old club. The eight-game sample is not a clean laboratory. But it is the sample we have, and it points one way.

That the pair are both wanted elsewhere this week — Saudi interest in Júnior and in Vanja Mačkić has surfaced — only sharpens the question of how the left is meant to fit together. Júnior's display in Europe, meanwhile, has reminded everyone what the flank looks like when it clicks.

The verdict from the numbers is blunt: strong without, struggling with. Chelsea's unbeaten run can carry a partnership for a while. It cannot carry one forever.