Jose Mourinho's dreams of winning the Champions League with Chelsea suffered an early setback on Wednesday when the Londoners fell to a shock 2-1 home defeat by Swiss champions Basel in their opening Group E match.
Chelsea, beaten in the Premier League by Everton on Saturday, looked short of ideas all night in a stuttering display, though they led 1-0 following a neat finish by Oscar just before halftime.
The Brazilian hit the bar soon after the restart as Chelsea briefly turned on the style but they were never able to take complete control and Mohamed Salah equalised in the 71st minute.
Basel, beaten by Chelsea in the Europa League semi-finals last season, grew in confidence and scored again 10 minutes later when captain and centre forward Marco Streller cleverly glanced in a near-post header from a corner.
Chelsea gave a debut to 30 million pounds ($47.9 million)signing Willian and a first home start for 20-year-old Marco Van Ginkel but they were pedestrian and disjointed for most of the first half.
A neat pass by the ever-aware Lampard enabled Oscar to give them a flattering halftime lead and their formidable home record in the competition looked safe.
Basel, who took four points off Manchester United in the Champions League in the 2011-12 season, were always in the game and it was no real surprise when they levelled after Salah played a nice one-two with Streller and curled in a confident low shot.
They went close again soon after through Streller but Chelsea failed to heed the warning and the big forward got in front of Gary Cahill to head the winner nine minutes from the end.
With Schalke 04 and Steaua Bucharest making up the group the defeat should not necessarily be terminal for Chelsea, who failed to get out of their group last year, but it was not the start Mourinho had planned when he returned to the club from Real Madrid three months ago.