Arsene Wenger feels the 4-1 victory at Tottenham proves Arsenal have every intention of going all the way in the Carling Cup this season, but admits concern over a metatarsal injury to England defender Kieran Gibbs.
Teenager Henri Lansbury - one of eight changes by Wenger, who was serving a one-match touchline ban - swept the visitors ahead from close range on 15 minutes.
Robbie Keane, who came on at half-time, scored an equaliser three minutes after the restart to level for a much-changed Spurs side, which saw Brazilian midfielder Sandro make his debut.
However, neither team could find a winner in normal time, with Samir Nasri's penalty double and Andrey Arshavin's goal sending the Gunners through.
Left-back Gibbs, 20, hobbled out during the first period of extra-time with what could be another serious metatarsal problem, the youngster having missed a large part of last season and with it the chance to feature at the World Cup because of a similar injury.
Wenger hopes the prognosis is positive on Gibbs, who was handed his senior international debut in the friendly against Hungary at the start of the season.
"We have to check, that is the only disappointment of the night, because Gibbs had a very good game," said the Arsenal manager.
"We hope we do not get bad news on Wednesday.
"It is a metatarsal again, it is the one next to the one he had broken, the second one, so we hope we have good news, because that would be a massive blow to us."
Wenger had named a strong side for last night's tie, with the likes of Arshavin and Marouane Chamakh on the bench.
"We have got a few reproaches that we did not take the competition seriously, it was a derby and to go out straight away for us would be difficult," said the Gunners boss.
"If everybody is fit, I can go as well for this competition.
"I have always said that the big competition you really count are the Champions League and the [Premier League] championship.
"I maintain that, but I want to win every single game I play with my team."
Wenger watched from the stands, having yesterday accepted a misconduct charge and fine by the Football Association following his actions at the end of the game at the Stadium of Light when Arsenal conceded an equaliser in the fifth minute of stoppage time.
"I accepted the FA charge because what I was charged with I did," the Frenchman said.
"I could not deny it, so that is why I took it.
"I could appeal but thought it was better to get it behind me.
"It was quite enjoyable to watch it from upstairs. Communication was a problem sometimes, but overall it went well."
Spurs boss Harry Redknapp admitted it was in the end too much of an ask for his much-changed side, but believed it was a worthwhile exercise.
"We made 10 changes, they made eight, but it was a chance for those lads who had not played, because they needed to play," he said.
"I was picking the players I needed to play - I can't keep playing the same people, you end up killing them off in the end."