While defending champions Barcelona secured top spot in Group H after emerging with a 3-2 victory from an engaging encounter with AC Milan at San Siro.
After Manchester City and Manchester United had stuttered on Tuesday, it was left to the London sides to restore English pride 24 hours later.
A Robin van Persie double saw Arsenal keep their side of the bargain by beating German champions Dortmund 2-0, but Chelsea must now win at home to Valencia in their final game to be sure of a last-16 place.
The breakthrough arrived four minutes into the second period and stemmed from an unlikely source, with Alex Song weaving past three Dortmund defenders on the Arsenal left before crossing for van Persie to head home.
The in-form Dutch striker tapped in his second from Thomas Vermaelen’s flick-on in the 86th minute, before Shinji Kagawa claimed an injury-time consolation for the visitors.
Marseille would have joined Arsenal in the last 16 had they not fallen 1-0 at home to Olympiakos.
At Leverkusen’s BayArena, Chelsea saw former player Michael Ballack hit the crossbar with a first-half header before Didier Drogba broke the deadlock from Daniel Sturridge’s pass after three minutes of the second half.
Ballack then drew two fine saves from former team-mate Petr Cech as Chelsea closed in on a place in the next round, only for Eren Derdiyok to dispatch Sidney Sam’s cross and claim a 73rd-minute equaliser.
Worse was to follow, as Manuel Friedrich headed home from an injury-time corner to take Leverkusen into the last 16 and leave Chelsea facing a winner-takes-all showdown against Valencia on December 6.
The Spaniards moved into contention after a dominant display, with Roberto Soldado netting a first-half hat-trick in a 7-0 rout of Genk.
At the San Siro, Barca old boy Zlatan Ibrahimovic had cancelled out Mark van Bommel’s own goal for his own former club, Lionel Messi put the visitors in front with a twice-taken penalty in the 31st minute.
Kevin-Prince Boateng slammed home a sublime equaliser, only for Xavi to claim a 63rd-minute winner from Messi’s pinpoint pass.
In the other group game, Viktoria Plzen climbed off the bottom of the pool with a 1-0 win at BATE Borisov.
Earlier, APOEL Nicosia became the first Cypriot team to reach the knockout phase after they drew 0-0 at Zenit Saint Petersburg in Group G.
Porto defeated Shakhtar Donetsk 2-0 to help the Portuguese champions go through if they win at home to Zenit in their final group game.