A sucker punch from Robert Lewandowski consigned Arsenal to a 2-1 defeat at the hands of Borussia Dortmund in the Champions League.
Dortmund took the lead when Aaron Ramsey was dispossessed on the edge of his own penalty area, Lewandowski laying the ball off to Henrik Mkhitaryan who fired past Wojciech Szczesny from the edge of the penalty area.
But Olivier Giroud drew the hosts level from point blank range when a devilish cross from Bacary Sagna provoked a mix up between Neven Subotic and Roman Weidenfeller as the sides went in level at the break.
Lewandowski was perhaps fortunate not to get a straight red card after elbowing Laurent Koscielny in the face as Arsenal built up a head of steam, Santi Cazorla hitting the bar with a rasping shot from range.
Just nine minutes remained when Dortmund fled upfield, Kevin Grosskreutz crossing for Lewandowski to convert on the volley at the back post and seal three points for last year's runners-up.
A double from Fernando Torres helped Chelsea cruise to a 3-0 victory in Schalke as Jose Mourinho's side roared back into contention in Group E.
Torres put Chelsea ahead after just five minutes, nodding home from a corner after Branislav Ivanovic's flick on. And he got his second after a fine Chelsea breakaway, as Eden Hazard and Oscar combined to tee the Spaniard up.
With Schalke chasing the game, Hazard then engineered another breakaway, this time choosing to shoot himself and slotting a precise shot into the far corner.
AC Milan and Barcelona shared the spoils in a thrilling match at the San Siro.
Milan edged ahead inside ten minutes when Robinho capitalised on some poor Barca defending and swapped passes with Kaka before finishing from close range.
But Lionel Messi drew the visitors level soon after, cutting inside from the right flank before sliding a low shot into the bottom corner.
Both sides had chances to pinch a winner -- Andres Iniesta forcing a desperate save from Marco Amelia, while Robinho miscontrolled inside Barca's penalty area with only Victor Valdes to beat.
Celtic stunned Ajax in Glasgow with a 2-1 victory that leaves them well placed in Group H, thanks to Milan and Barca's draw.
James Forrest grabbed their first from the penalty spot after Stefano Denswil had fouled Anthony Stokes before Baram Kayal's shot from range took a deflection to find the bottom corner.
Lasse Schone registered a consolation goal for Ajax deep into stoppage time with a fierce strike from range after Celtic's Nir Biton had been shown a straight red card for a lunging challenge but the home side saw out the game to seal another famous win.
Atletico Madrid breezed past Austria Vienna with an emphatic 3-0 victory at the Franz Horr Stadium.
Atletico cruised into a two-goal lead inside 20 minutes in Vienna, Koke's pass releasing Filipe Luis into the area and he squared for Raul Garcia to tap home.
Twelve minutes later Diego Costa doubled Atletico's advantage, charging from inside his own half before finding the net and the Brazilian put the gloss on the result by finishing neatly from Emiliano Insua's cross.
Napoli saw out a nervy final few moments in France as they secured a 2-1 away win at Marseille.
Jose Maria Callejon put the Italians ahead shortly before half time, latching on to a Gonzalo Higuain pass before cutting inside and finding the net.
Then substitute Duvan Zapata scored with his second touch, rifling a rocket of a shot into the top corner from 25 yards out, to leave Napoli comfortable.
Marseille gave themselves a sniff of a draw after Andre Ayew ran on to a pass from brother Jordan to loop a shot over Pepe Reina but Rafa Benitez's side held on for the win.
Porto sunk to a 1-0 home defeat at the hands of Zenit St Petersburg thanks to Alexander Kerzhakov's late goal.
Hector Herrera was sent off inside six minutes after picking up two yellow cards in the space of 20 seconds -- one for a foul and the second for encroaching from a free kick.
Porto held on until six minutes from time when Kerzhakov found some space inside the area and nodded home Hulk's cross.
A late equaliser from Leandro Tatu earned a point for Steaua Bucuresti as they drew 1-1 with FC Basel in Romania.
Marcelo Diaz's precise curling shot put the Swiss side ahead just after half time but Tatu stole in to finish from a low ball into the area as Steaua grabbed their first point of the competition.