Chelsea great Pat Nevin praised Arsenal's performance in their 2-0 win over Monaco on Tuesday but felt it all went wrong in the first leg.
Nevin blamed the Gunners' lack of concentration during the initial bout at the Emirates Stadium for their exit from the Champions League at the Round of 16 stage.
Arsenal were brilliant as they defeated Monaco in France but the third goal they conceded back in London cost them dearly in the end.
Nevin told BBC Sport: "The default position when a team gets knocked out of Europe is to have a dig, to have a go. But Arsenal did so well tonight.
"They put together a brilliant 90 minutes, getting two goals away from home against a team that doesn't concede goals. But this is a rarefied atmosphere.
"A lack of concentration at the end of the first leg lost Arsenal this tie."
