Mohamed Salah scored a breakaway goal in the 87th minute as Basel beat Chelsea 1-0 to complete an unlikely Champions League double over the Londoners on Tuesday.
Goalkeeper Petr Cech produced a string of outstanding saves in the first half to keep the dominant Swiss team at bay.
Basel, for whom Salah scored in a 2-1 win over Chelsea away earlier in the campaign, then struck the winner when the Egyptian broke down the left before sliding the ball past Cech into the corner of the net.
"Salah is a pacy and good player. He caught the defence napping," Chelsea's Portuguese coach Jose Mourinho told Al-Jazeera sports after the game.
Leaders Chelsea have nine points from five games in Group E and have still qualified for the knockout stages.
Basel are second on eight points while Schalke 04 are third on seven points after drawing 0-0 at bottom club Steaua Bucharest.
Cech kept Chelsea in the game in the opening period while opposite number Yann Sommer did not have a single shot to warm him up on a freezing night.
The visiting keeper did well to keep the ball out in the third minute when Marco Streller got a touch to Valentin Stocker's inswinging free kick and he was tested again by a low, deflected Fabian Frei effort in the 13th.
Cech then tipped over a powerful effort from Salah before producing a superb stop to deny the lively Egyptian.
The Czech keeper was going the wrong way and his sight was blocked by defenders but he still managed to raise his arm to turn the ball away at the last minute.
Chelsea had another let-off when John Obi Mikel cleared off the line from an inswinging corner and they also survived a penalty appeal when the ball struck Frank Lampard's outstretched arm.
The Londoners were below par throughout and it came as no surprise when Salah struck late on.
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