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 after 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.
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.
- Engrossing affair -
The Arsenal and Bayern match was an engrossing affair for the first-half -- Arsene Wenger having taken the bold decision to start the raw young French striker Yaya Sanogo up front instead of the vastly more experienced Olivier Giroud -- with Mesut Ozil seeing former schoolmate Manuel Neuer saving his early penalty.
However, with the match evenly-poised Arsenal, like their Premier League title rivals Manchester City against Barcelona on Tuesday, went a man down when Szczesny was sent off -- the Gunners' 100th red card under Wenger.
The Pole did himself few favours with UEFA by making an offensive gesture as he entered the tunnel but Arsenal were not punished from the spot as David Alaba's penalty hit the post.
However, they finally cracked in the 53rd minute as Kroos's superbly struck right-foot curler gave Lukasz Fabianski no chance.
Whilst Bayern huffed and puffed to get what would probably be a killer second away goal, Arsenal staged a superb backs to the wall defensive performance, although they were perhaps fortunate not to concede another penalty when Laurent Koscielny appeared to take substitute Thomas Mueller's legs from under him.
However, two minutes from time - eerily also like the City loss to Barcelona - they conceded a second as Mueller was on hand to head the ball home.
"Arsenal were much 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."
Wenger bemoaned what he saw as his side not having luck run their way.
"Everything went against us. We should have been 3-0 up before they got a sniff in the game," he said.
"We had more problems in the second half with 10 men because they have very good players."
In the other game Milan had started the brightest against Atletico.
First Brazilian Kaka saw his long range effort cannon off the bar then Andrea Poli's header -- after being set up by the lively Adel Taarabt making his Champions League debut -- came back off the woodwork as well.
The early fireworks were not a forestaste of what was to come as the match petered out with Milan's problems growing as star striker Mario Balotelli went off clutching his shoulder late in the second-half.
Shortly after that Atletico struck as Diego Costa headed home to give the Spaniards a superb chance of reaching the quarter-finals and end Italian interest in the competition.