Neil Harris praised the atmosphere inside The Den, calling it the "best in football" after Millwall dumped Everton out of the FA Cup.
Everton scored from both of their shots on target through Richarlison (43) and Cenk Tosun (72) but despite leading twice, Everton could not hold on to their advantage as Lee Gregory (45+1) and Jake Cooper (75) pulled the Sky Bet Championship side back into the match.
A replay looked on the cards but Millwall mustered one last attack in stoppage time and Murray Wallace fired home (90+2) after some dismal Everton defending.
Harris hailed the victory as a "great scalp" as they knocked a Premier League side out at The Den for the fifth time in a row.
"It's big for the football club - the fans galvanised us at key times," he said.
"We beat Bournemouth, Watford and Leicester but this is Everton, yes they're not having a great time but this is a huge club. It's a great scalp for us.
"The character my players showed to come from behind twice was special.
"I'd like anyone at home [in the next round]. It gives us an opportunity to win. I like my players to play in front of that atmosphere in big games.
"When this place gets going, there is no better atmosphere in English football. That was there today."
Everton boss Marco Silva was left fuming Cooper's goal - which levelled the game at 2-2 - was allowed to stand as replays suggested he prodded it home with his arm,
With no VAR in use, the goal stood.
Harris said: "At the time I thought Marco was moaning he was offside but Jake has been honest enough to say the ball came off his arm. If we've got a bit of fortune, we'll take that."