Chelsea’s yo-yoing form is enough to give Jekyll and Hyde a bad name.

After a majestic, fluent display at Upton Park last weekend, the Blues travelled to Switzerland in midweek… and simply failed to generate any shred of excitement.

Without a single shot on target, the team relied on a string of Petr Cech saves to keep out Basel, right until three minutes from time, when a dazzling breakaway run allowed Mohamed Salah to score a late winner.

Perversely, other results meant that defeated Chelsea have qualified for the knockout stage of the Champions League, unlike last year when, as reigning champs, they made an undignified exit.

The poor showing in Toblerone territory contrasted sharply with Saturday’s breeze against West Ham, when two Frank Lampard goals (one from the spot) and an Oscar daisy-cutter gave the Blues a surprisingly simple victory.

Worryingly for Chelsea, they face Southampton on Sunday without striker Samuel Eto’o, stretchered off in Basel with a muscle problem.

Fernando Torres came on in his place as sub, but it leaves Jose Mourinho short of options as the Blues face a gruelling nine games in 29 days through December.

Jose attributed the Swiss rollover to tiredness, which surely opens the door to more appearances by fans’ favourite Juan Mata, an unused sub at both West Ham and Basel.

Several continental sides are circling like vultures, waiting to see if Mata becomes so disenchanted with his lack of play in a World Cup season that they might be able to tempt him away.

If Chelsea do lose their beloved midfielder – deserved winner of the club’s player of the year prize for the past two seasons – it would be a serious blow.

Despite his reassuring words, Mourinho seems to harbour doubts about the 25-year-old, theoretically contracted to Chelsea until 2018.

He will be expected to start this Sunday and – if the Saints’ halos crack – in a few more December matches too.