Ronnie Moore insisted non-league Eastleigh deserved to upset League One Swindon - after masterminding a 3-1 shock win.
Jai Reason, Andy Drury and Mikael Mandron’s penalty handed the National League side, who include former Sheffield Wednesday favourite Reda Johnson in their ranks a place in the second round.
Moore said: “We have played them off the park. It was unbelievable when you consider they are a League One club.
“They beat Charlton on Saturday but for us to come and perform the way we did today it is defies belief. We believed in ourselves but this was a fantastic night for Eastleigh.
“We couldn’t get any better than the first half, we knew we wouldn’t improve, but it was all about counter-attacking them. When they gave the ball away we hit them and we could have won by more. They have only scored because we were being stupid and lackadaisical.
“Our hearts were in our mouths for the last 10 minutes and if they had got something out of the game we would have been sick.
“To beat a League One team when you are a non-league team is fantastic for me and the team. It is fully deserved. We are in the second round now, it isn’t quite Wembley.”
Winger Reason got the victory going in the 16th minute when he clipped in, following a one-two with Scott Wilson.
Drury doubled the lead 10 minutes before half-time with a cool finish, before former Sunderland striker Mandron bagged his 13th goal of the season from the penalty spot after Wilson was dragged down by Brandon Ormonde-Ottewill.
Nathan Delfouneso pulled a goal back - but it is the fifth year in a row the Robins have been dumped out in the first round.
Head coach Luke Williams said: “It was men against boys tonight. As a team with hundreds of games behind us. It showed tonight and we struggled to keep the intensity that we showed at the weekend.
“We came off second best. Eastleigh were excellent and managed the game very well.”
Tim Sherwood joined Williams on the touchline for the first time since being unveiled as the Wiltshire club’s director of football.
Williams added: “He wanted more input from the side. No one was surprised. He wants to help in every way.
“There will have to be more hard work and the players need to quickly get on board with plenty of new ideas that Tim has brought to the club.
“We all have to perform week in and week out and if we don’t we can expect to be replaced.”