|The pressure is on Chelsea's André Villas-Boas as his new team also find themselves 12 points behind leaders Manchester City in the English Premier League [GETTY]
Arsenal reached the European Champions League knockout phase with victory over Borussia Dortmund on Wednesday, but Chelsea were made to wait after a dramatic 2-1 defeat at Bayer Leverkusen.
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.
Dortmund lost both Sven Bender and star man Mario Goetze to injury inside the first 30 minutes at Arsenal's Emirates Stadium but the hosts were unable to capitalise in what proved to be an underwhelming first half.
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, with Ioannis Fetfatzidis' 83rd-minute half-volley keeping alive the Greeks' chances of securing a knockout round berth.
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.
"It's tough for the English clubs in the Champions League at the moment but we have to put on a brave face," said Chelsea coach Andre Villas-Boas, whose side have lost three of their last five games.
"We are still in front of Valencia and expect Leverkusen to do their job (against Genk). We can go through."
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.
|Barca clinch top spot in Group H with their win [EPA]
After 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, cushioning a high ball before flicking it past Eric Abidal and beating Victor Valdes at his near post, 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, in a game temporarily halted twice after home fans threw flares onto the pitch.
"It's a fantastic result for us," said APOEL coach Ivan Jovanovic, whose side were cheered on by a 2,000-strong band of hardy followers.
"We're trying to play attacking football. We may be a small team if compared to the European giants but we're a team with a big heart."
A late Hulk strike and a Razvan Rat own goal gave Porto a 2-0 win at Shakhtar Donetsk that means the Portuguese champions will go through if they win at home to Zenit in their final group game.