Arsenal's miserable week continued as runaway Bundesliga leaders Bayern Munich produced a European masterclass at the Emirates to take a commanding 3-1 Champions League first leg lead.
The Gunners, who crashed out of the FA Cup at home to Championship Blackburn at the weekend, were behind after only seven minutes when midfielder Toni Kroos hammered home a shot from the edge of the box.
Thomas Muller stabbed home from close range to double Bayern's advantage with 21 minutes played.
Arsenal were booed off at the break but rallied when striker Lukas Podolski headed home against his former club.
However, the Germans cut through again on 77 minutes as Mario Mandzukic scrambled in a third, leaving Arsenal facing a huge task to find a way back into the tie.
Porto earned themselves a narrow 1-0 lead in the home leg of their clash with Malaga thanks to a second-half Joao Moutinho strike.
The Portuguese league leaders had the better of possession throughout but were frustrated by their La Liga opponents' defensive organisation.
They could have taken the lead early in the second half when Alex Sandro sent over a cross from the left and the stretching Marat Izmailov almost turned it home.
But the breakthrough came when Sandro made space to cross and found Moutinho, who swept the ball in with a fine first-time finish.