Captain Cesc Fabregas insists Arsenal can still fight their way past FC Porto and into the quarter-finals of the Champions League.
The Gunners left Estadio do Dragao on the end of a controversial 2-1 defeat to leave their European hopes hanging in the balance.
Goalkeeper Lukasz Fabianski had an evening to forget, as the young Pole first pushed Silvestre Varela's cross into his own net before then giving away a free-kick when he picked up a back-pass from Sol Campbell which set up Porto's second goal.
However, given the Gunners managed to grab what could be a crucial away goal through Campbell's header, Fabregas insists all is not lost ahead of the second leg at the Emirates Stadium in a fortnight's time.
"It is going to be hard for us in the second leg, but I am still confident we will prevail in the end," the Spain midfielder said. "We will just have to see who's strongest on the night."
Porto lost 4-0 at Arsenal in the group stages last season, and were beaten home and away by Chelsea earlier in the current European campaign.
Fabregas added: "We knew Porto had a very quick and talented team, but the truth is we allowed them to score two very easy goals.
"You just can't let that happen at this level. Now we are 2-1 down and we are going to have to fight our way back."
As well as missing first-choice goalkeeper Manuel Almunia because of a finger injury, Arsenal were also without defender William Gallas, midfielder Alex Song, Russian playmaker Andrey Arshavin and Croatia forward Eduardo.
Manager Arsene Wenger expects Almunia to miss Saturday's Premier League game with Sunderland, but Arshavin could be back from his hamstring problem.
