Chelsea have struck late with a header by defender Marcos Alonso to beat a stubborn Slavia Prague side 1-0 in their Europa League quarter-final first leg, while cross-town rivals Arsenal outclassed Napoli.
Alonso broke the deadlock for the Blues in the 86th minute of Thursday's clash, sneaking behind two defenders to connect with Willian's cross.
Chelsea manager Maurizio Sarri made seven changes to his line-up from the team that beat West Ham 2-0 in the Premier League on Monday, with talisman Eden Hazard coming off the bench for the last half-hour.
"I'm very happy with the result and also with the performance, because at this moment we are able to suffer, in the past we were not," Sarri said.
"In the past, when we were in trouble, we conceded immediately a goal.
"Now, we did not concede anything."
Arsenal, meanwhile, earned a 2-0 win over Napoli to take control of their tie.
Aaron Ramsey's first-half strike and a Kalidou Koulibaly own goal gave the Gunners a significant advantage over their Italian opponents in London.
Mesut Ozil started for the sixth straight game for Arsenal after regaining the trust of manager Unai Emery and was at the heart of most of their attacks.
"To keep a clean sheet and score a couple of goals is a lovely way to start the first leg, we're delighted with that," Ramsey told British media.
"We can go into the second leg with a little bit of a cushion but we know it will be a difficult place to go - they are a quality team."
The Neapolitans have now failed to beat English opponents away from the San Paolo stadium in nine attempts in European competition, and will need to be on scoring form at home if they are to progress in the competition.
Elsewhere, Valencia beat local rivals Villarreal 3-1 against the run of play, while Benfica scored a 4-2 win over 10-man Eintracht Frankfurt, with 19-year-old Joao Felix becoming the youngest player to score a Europa League hat-trick.
The second legs take place on April 18.