Chelsea boss Maurizio Sarri admitted some relief after surviving a Slavia Prague fight-back to win 4-3 in Thursday night's Europa League quarterfinal second-leg.

Chelsea reach the semifinals 5-3 on aggregate.

Sarri's side were cruising at half-time with a four-goal aggregate lead before Petr Sevcik produced two sensational strikes as the nerves crept into a previously dominant Chelsea performance.

Buoyed by their noisy supporters, the visitors pushed forward as they tried to force a way back into the game but time defeated them as the Blues regained their composure to close out victory.

Having secured a valuable 1-0 advantage in the Czech Republic, Chelsea raced into a three-goal lead in west London courtesy of goals from Pedro, Olivier Giroud and a calamitous Simon Deli own goal.

Slavia captain Tomas Soucek headed in his side's first goal before Pedro doubled his tally just 63 seconds later.

Chelsea travel to Germany for the first leg of their last-four tie with Eintracht Frankfurt on Thursday, 2 May.

Sarri said, "We started very badly in the second half but I'm really really happy because we played well in the first 45 minutes and we are in a European semi-final which is very important to us.

"We knew very well the match was going to be difficult. They ran a lot and with quality - lot of metres at high speed."