Blues hold the advantage going into return fixture at Stamford Bridge, despite contentious penalty.
Chelsea interim boss Rafa Benitez has questioned the decision to award FC Basel a late spot kick in their Europa League semi-final first leg at St. Jakob-Park on Thursday night.
The West London club were leading 1-0 when referee Pavel Kralovec gave the home side a highly-debatable penalty following a challenge in the box by Chelsea defender Cesar Azpilicueta on Valentin Stocker.
However, despite the Swiss outfit levelling matters up from the spot, the visitors then won the match 2-1 thanks to a last-minute free kick from David Luiz.
Watch Benitez’s post-match press conference below: