Substitute Eden Hazard saved Chelsea's blushes with a stoppage-time strike that saw Rafael Benitez's side sneak into the Europa League last 16 with a 1-1 draw against Sparta Prague that sealed the tie 2-1.
The reigning European champions were behind after just 17 minutes as David Lafata fired home from close range, while Fernando Torres was guilty of missing several key chances to put the tie to rest, with Tomas Vaclik in the Sparta goal able to the task.
Hazard grabbed the all-important goal to avoid extra time and, more pertinently, the potential of an embarrassing Europa League exit on home turf.
Victor Moses took just four minutes to create the night's first chance, although his pull-back was directed wide by Torres. Oscar then saw a hopeful long-range effort deflect behind before Torres hooked an excellent Juan Mata cross onto the roof of the net.
Torres was getting a lot of the early action and also headed over, with Vaclav Kadlec producing Sparta's only real threat. The visitors, though, netted the opener when Kadlec gathered a quick free-kick in the box and jinked past Gary Cahill before laying off for Lafata to rifle home from close range.
The visitors were in the driving seat, with Petr Cech forced to save a low strike from the unmarked Tomas Prikry. Marek Matejovsky volleyed over from the resulting corner and, after a break in play for referee Aleksandar Stavrev to receive treatment, Lafata twice tried - and failed with - long-range efforts.
Chelsea ended the first half on top, though, as Mata met a Ramires ball over the top with a tremendous touch only to see his goalbound strike pushed over by the Sparta goalkeeper. Ramires took just two minutes of the second half to rattle the Sparta goal frame, after latching onto a ball from Oscar, before Moses struck wide from 25 yards.
Torres then raced beyond the Sparta backline but his dinked effort was thwarted by Vaclik. The Sparta Prague goalkeeper then denied John Terry who attempted a flick over his shoulder. Sparta almost capitalised, with captain Matejovsky breaking through the middle only to fire just wide of Cech's far post.
Benitez replaced Oscar with Hazard - a change met by boos from the home support - as Chelsea upped the ante in the closing 15 minutes in a bid to avoid extra time, with a Hazard free-kick almost sneaking in, before Cesar Azpilicueta and Ramires blazed over.
Kadlec twice came close in stoppage time, before the travelling fans' hearts were broken. Substitute Hazard was the man who did the damage, finding space in the left-hand side of the box to fire home a stoppage-time leveller and put Chelsea through 2-1 on aggregate.