Holders Bayern Munich and Spanish side Atletico Madrid took large strides towards the quarter-finals as they secured precious away wins in their Champions League last 16 first-leg ties on Wednesday.
Bayern beat Arsenal 2-0 with both their goals coming in the second half.
The hosts had been reduced to 10 men shortly before half-time when Polish goalkeeper Wojciech Szczesny was sent-off for a rash challenge on Arjen Robben.
Toni Kroos and Thomas Mueller struck for the visitors – the duo having also netted in the 3-1 win a year ago to the day against the same opponents in London – and Arsenal will have to repeat at the very least their 2-0 win in the away leg last year to hold any hope of progressing.
“Arsenal were much better than us in the first 15 minutes and after the goalkeeper was sent off the game changed,” said Bayern coach Pep Guardiola.
“However, it was not easy for us with nine Arsenal players in their penalty area but we played patiently and in the end we broke them down.
“Last year Bayern had a better result than this evening and in the end it was a very close run thing.
“It will depend on our heads in Munich but we will play to win.”
Atletico gave themselves a great chance of making the quarter-finals for the first time in 17 years as a fifth goal of the campaign by Diego Costa seven minutes from time gave them a 1-0 win over Italy’s last representatives AC Milan.