Jose Mourinho's first Champions League tie since returning to Chelsea ended in disappointment as Swiss champions Basel earned a shock win at Stamford Bridge.Oscar put Mourinho's side ahead with an angled first-time shot into the bottom corner at the end of the first half.Basel's Mohamed Salah levelled when he fired across Blues keeper Petr Cech. And the home crowd was left stunned as away skipper Marco Streller won the Group E opener for the visitors with a late near-post header.In other results:Marseille 1-2 ArsenalMilan 2-0 CelticBarcelona 4-0 AjaxSchalke 3-0 Steaua Bucharest