City shifted 8,000 tickets for the Capital One Cup final within two hours of them going on sale.
Director of operations David Baldwin revealed that the club sold around 6,000 online and a further 2,000 by phone between this morning's 9am start and 11am.
But he has also repeated the plea for fans to "stay calm and be patient".
Some supporters have found themselves timed out waiting for orders to go through - which the club say is down to the sheer volume of demand.
He said: "We aren't going to sell out. The system is holding up well but it's the desperation to get 20,25 or 30 tickets in blocks at the same time.
"Be pragmatic about it. People should be happy just to be in the stadium for this amazing occasion.
"Ideally I know they would all like to sit together but when you are trying to get blocks of that many together that is what is causing the delays."
City have been allocated 31,852 tickets for the game against Swansea on Sunday, February 24.
Season ticket holders have a two-week window until 5pm on Wednesday, February 13. After that, the remainder are expected to go on general sale.