JOIN USRubin rock Nou Camp
Inter Milan were held to a 2-2 home draw by Dynamo Kiev while Fiorentina won 4-3 at Debrecen, where six goals came in the first 37 minutes.
Sevilla made it three wins in a row with a 3-1 success at VfB Stuttgart but Arsenal were denied their third successive win by a last-minute equaliser for AZ Alkmaar in a 1-1 draw.
Barcelona fell behind after two minutes at the Nou Camp when Aleksandr Ryazantsev scored from long range.
Zlatan Ibrahimovic equalised in the 48th minute but Gokdeniz Karadeniz restored the visitors' lead 20 minutes from time and, despite a series of late attacks, Barca could not prevent their first defeat in the competition in 10 games.
Inter's dire Champions League run continued as they failed to win for the eighth game in a row and were somewhat lucky to escape with a point, having twice come from behind.
Taras Mikhalik (5th) and a Lucio own goal (35) twice had Dynamo ahead with Dejan Stankovic and Walter Samuel replying.
The results leave Group F, which had looked a two-horse race at the start, too close to call with Barcelona, Kiev and Rubin all on four points and Inter on three after three draws.
An injury-time goal by Cesar Delgado put Lyon in control of Group E and left Liverpool's hopes hanging by a thread. Five-time European champions Liverpool, already struggling without injured striker Fernando Torres, lost injured captain Steven Gerrard after 24 minutes but went ahead through Yossi Benayoun late in the first half.
Lyon substitute Maxime Gonalons headed in a deserved equaliser after 72 minutes before Argentine forward Delgado finished off a sharp breakaway to hand Liverpool a fourth successive defeat in all competitions and leave them third on just three points.
Lyon in command
Lyon are well placed with a maximum nine points ahead of second-placed Fiorentina on six after their goalfest at Hungary's Debrecen, who are pointless after three defeats.
Sevilla are also on nine points after two goals from defender Sebastien Squillaci and one for Jesus Navas gave them an impressive Group G success in Germany.
Romanian champions Unirea Urziceni are the unlikely second-placed side on four points. They secured a first European win by embarrassing Rangers 4-1 in Glasgow -- helped by two own goals and a missed penalty from the generous hosts.
Stuttgart have two points and Rangers, who were booed off at Ibrox, one.
Arsenal also looked on course for a third successive win until David Mendes da Silva grabbed a stoppage time equaliser to earn Alkmaar a point.
Cesc Fabregas had put Arsenal ahead in the 36th minute but they paid the price for sitting on their lead in the second half.
Arsenal remain top of Group H on seven points with Olympiakos second on six after they also scored in added time to beat Standard Liege 2-1.
Liege led through Igor De Camargo but Kostas Mitroglou headed an equaliser and substitute Ieroklis Stoltidis struck the winner in the 93rd minute.