ROME - Arsenal's mental strength has been called into question recently but coach Arsene Wenger said it was a key factor in his young side's penalty shoot-out victory over Roma in the Champions League on Wednesday. Arsenal prevailed 7-6 in the shoot-out after Roma's Brazilian defender Juan's early goal had cancelled out the Londoners' 1-0 advantage from the first leg. "After missing the cross to concede the goal and missing the first penalty, we needed something special to come back and win," Wenger told a news conference. "I'm very proud of our mental strength because that's a quality that has been questioned in our team, but you can see we've improved tremendously on that front. "I was a bit concerned that if we were the only (English) team to go out, it would halt the team's progress. This kind of result can increase self believe and results for the rest of the season." England have four teams -- Arsenal, Manchester United, Liverpool and Chelsea -- in the last eight for the second consecutive year while Italy are left without a representative. "England can be very proud to have four teams in the quarter-finals again, but don't be fooled by the three Italians getting knocked out," said Wenger. Roma coach Luciano Spalletti was satisfied with the performance of his side, who were without several regulars due to injury, illness and suspension. "We have to be proud of what we've done, while knowing that we can still improve." The hosts were unlucky not to get a penalty before halftime when Motta went down after a clumsy challenge by Gael Clichy. "I haven't seen a replay yet, but from the bench it looked like an penalty," he said. "But the penalty wasn't given and we must accept the referee's decision, even if it's with some bitterness."