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 halftime 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.
"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."
Wenger bemoaned what he saw as his side not having luck run their way.
"We had more problems in the second half with 10 men because they have very good players," he said.
In the other game Milan started the brightest against Atletico but the early fireworks were not a sign of what was to come as the match petered out.
Atletico finally broke the deadlock as Diego Costa headed home to give the Spaniards a superb chance of reaching the quarter-finals and end Italian interest in the competition.
Atletico's Argentinian coach Diego Simeone said that his side had improved after a wobbly start.
"Milan were full on and aggressive, especially after the first 10 minutes," Simeone said.
"We realised that one error in such a tight match could be costly and we took advantage of one to win."
His Milan counterpart, another former great midfielder Dutchman Clarence Seedorf was far from downcast about their chances of turning things round.
"I am very happy with what I saw this evening and the guys are right to be optimistic and to believe they can win in Madrid."
