Gokdeniz Karadeniz celebrates his shock winner at the Nou Camp
Barcelona suffered one of the biggest shocks in the history of the Champions League group stages against Rubin Kazan, while Sevilla qualified for the next round after just three matches.
BBC Sport rounds up all the action from across Europe in the third round of Champions League group games.
Six of the seven goals came in the first half in Hungary.
Peter Czvitkovics gave the hosts an early lead after converting a Jozsef Varga cross, but a fine finish from former Chelsea striker Adrian Mutu soon levelled the game.
Mutu then turned provider for Alberto Gilardino who calmly slotted home after 10 minutes, with Gilardino returning the favour by setting up Mutu to drill home from outside the box shortly after.
Gergely Rudolf curled into the top corner to bring Debrecen back to 3-2 but a powerful left-footed shot from Mario Santana restored the Italians' two-goal cushion just before the break to cap an incredible first half.
Adamo Coulibaly headed home for the hosts late on to set up a grandstand finish, but Fiorentina held on for the points.
GROUP F
In an incredible night of action, Barcelona suffered an amazing 2-1 home defeat to Rubin Kazan, while Inter Milan were held to a surprising 2-2 draw by Dynamo Kiev.
There is now a three-way tie for top spot in the group table, with Kazan, Barcelona and Kiev all on four points. Jose Mourinho's Inter are rock bottom with only three points from their three games.
But the result at the Nou Camp will send shockwaves around the footballing world after Kazan pulled off one of the greatest upsets in club football history.
Aleksandr Ryazantsev gave the visitors a shock lead after just two minutes, picking up the ball and letting fly from 25 yards with a stunning drive that flew into the top corner - the fastest ever Champions League goal scored by an away team at the Nou Camp.
Zlatan Ibrahimovic equalised with his first Champions League goal for his new club early in the second half after being set up by Xavi.
But Gokdeniz Karadeniz finished off a superb breakaway move following a mistake in the Barcelona midfield late on to stun the reigning European champions.
At the San Siro, Taras Mykhalyk gave Kiev the lead after five minutes before Dejan Stankovic smashed home an equaliser for Inter on the half-hour.
An own goal from Lucio restored the visitors' lead but a Walter Samuel header secured a deserved draw for the Italian side just after the break.
Sebastien Squillaci headed the Spanish side into the lead after a fine cross from Adriano after 23 minutes - the defender's first Champions league goal in more than five years.
Jesus Navas made it two with a right-footed shot after 55 minutes before Squillaci (72) headed home his second to restore the cushion.
Brazilian Elson pulled one back for the hosts only a minute later but it was never going to be enough to stop a rampant Sevilla securing their passage to the next round.
GROUP H
Arsenal have had their lead at the top of Group H reduced to just one point after their 1-1 draw against AZ Alkmaar and Olympiakos' late 2-1 win against Standard Liege.
The Greek side looked in trouble when Liege took something of a surprise lead in the first half - Igor de Camargo slipping the ball past home goalkeeper Antonios Nikopolidis after being put through by Milan Jovanovic.
But a free-kick from Luciano Galleti was headed in by Kostantinos Mitroglou to bring the hosts back on terms and a late winner by Ieroklis Stoltidis sealed the victory, and prompted some wild celebrations from the home crowd.
The Greek side are now just one point behind the Gunners in the group table.
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