London - Chelsea were given a fright by Slavia Prague in a 4-3 home win on Thursday that saw them to a 5-3 aggregate victory and a place in the semi-finals of the Europa League.
Already 1-0 up from the first leg, Chelsea were cruising when they scored three more goals in the first 17 minutes at Stamford Bridge courtesy of Pedro, an own-goal by Simon Deli and Olivier Giroud and were 4-1 ahead on the night at half-time.
But having been facing a rout, the Czech visitors restored their pride with two early second-half goals from Petr Sevcik as they threatened a remarkable comeback.
Chelsea, however, held on and the London club will face Eintracht Frankfurt for a place in the final after the German side beat Benfica 2-0 to go through on away goals after the tie ended level at 4-4 after two legs.
Chelsea manager Maurizio Sarri made five changes from the team beaten 2-0 by Liverpool in the Premier League on Sunday and put Eden Hazard on the wing with Olivier Giroud the Blues' central striker.
The Londoners doubled their aggregate lead just five minutes into the second leg of this quarter-final tie thanks to Pedro's neat finish after a one-two with Giroud.
Minutes later, Chelsea had another goal.
Pedro produced a contender for miss of the season when presented with a tap-in from close range that came back off the post only for the ball to fly into the face of Slavia defender Simon Deli and rebound into the net for a bizarre own-goal.
Pedro then turned provider, squaring for Giroud to score his 10th Europa League goal of the season.
Chelsea were cruising at 3-0 ahead on aggregate and it seemed Tomas Soucek had done no more than score a consolation goal when he rose unmarked to head in from a corner.
Chelsea though were soon three goals ahead again when Pedro bundled the ball in.
But Slavia rallied impressively after the interval, with Sevcik's 20-yard shot beating Kepa Arrizabalaga at the Chelsea goalkeeper's near post.
And soon afterwards, in the 55th minute, Sevcik produced an even better effort from similar range that flew into the top corner to give Slavia hope of a remarkable recovery.
But that was as good as it got for the visitors, with Sevcik scuffing a shot that might have seen him complete what would have been an astonishing hat-trick.