Basel have come from behind to beat Chelsea 2-1 at Stamford Bridge in the Champions League group stage.
Chelsea started the match in control but the found it difficult to create many clear chances against a stubborn Basel side.
Eden Hazard linked well with Samuel Eto'o midway through the first half, but he wasted a good opportunity when he fired over from the edge of the box.
A quiet first period looked like it would end goalless but Oscar managed to break the deadlock when he slotted the ball into the bottom corner after collecting a through-ball from Frank Lampard.
Oscar was inches away from doubling his tally for the evening just a few minutes into the second half when he unleashed a powerful shot from long range, but the Brazilian was left frustrated when he saw the ball crash against the crossbar.
Hazard was picked out by Oscar in the box and the Belgian should have added a second for his side, but his disappointing performance continued when he blazed the ball over.
Chelsea were punished for not adding to their goal when Basel equalised in the 71st minute thanks to a well-placed strike from Mohamed Salah, who linked well with Marco Streller before beating Petr Cech.
Stamford Bridge was in shock with eight minutes left of normal time remaining when Cech failed to keep out a header from Streller after the forward had managed to lose his marker inside the Chelsea penalty area.
Chelsea did manage to create a chance late on, but Eto'o could not squeeze the ball in from a tight angle and Basel held on for the three points.