Defending champions Bayern Munich survived a shaky second half and missed a late penalty against Arsenal on Tuesday to reach the Champions League quarter-finals.
The holders looked less than all-conquering in a 1-1 second-leg draw against Arsenal who were left with too much to do after losing 2-0 at home in the opening match of the last-16 encounter.
Bastian Schweinsteiger broke the deadlock in the 55th minute before Bayern old boy Lukas Podolski replied almost immediately for Arsenal who grew in confidence and brought out goalkeeper Manuel Neuer's eccentric side.
The Bavarians won a controversial penalty when Arjen Robben reacted theatrically to a foul by Laurent Koscielny in stoppage time and Thomas Mueller's spot kick was superbly stopped by keeper Lukasz Fabianski, ending a run of 13 straight wins in all competitions.
In the other match of the night, Diego Costa extended his rich vein of form with a double as Atletico Madrid thumped AC Milan 4-1 to send the seven-times winners packing and secure a place in the Champions League quarter-finals for the first time in 17 years.
Costa, who struck in Atletico's 1-0 win at the San Siro in the first leg of the last-16 tie and has seven goals in five appearances in Europe's elite club competition, opened the scoring in the third minute with an acrobatic volley.
Kaka levelled with a header in the 27th as Milan briefly took control of the match before Arda Turan's deflected effort sailed into the net five minutes before halftime to restore the home team's lead.
Raul Garcia headed Atletico's third in the 71st minute and Costa struck again five minutes from time to seal a 5-1 aggregate success and crown a near-perfect night for the fans thronging Calderon stadium next to Madrid's Manzanares river.
Image: Bayern Munich's Thiago Alcantara and Franck Ribery (right) tackle Arsenal's Alex Oxlade-Chamberlain during their Champions League round of 16 second leg match in Munich, on Tuesday
Photograph: Kai Pfaffenbach/Reuters