Slaven Bilic hailed a "special night" in West Ham's history after the dramatic FA Cup win over Liverpool.
Angelo Ogbonna scored with a header in the last minute of extra time to secure a 2-1 victory and a fifth-round trip to Blackburn after a gruelling tie.
The Hammers were virtually on their last legs, having lost three players to injury and with at least two more limping through the final minutes.
But with the replay heading for a penalty shoot-out, centre-half Ogbonna was thrust into attack as a final throw of the dice and picked the perfect moment to head his first goal for the club.
"It was a special night," said boss Bilic. "There's no harm in saying that, it's a special night for our club and I'm proud and happy.
"I know it's only the last 16, but it's against Liverpool, it's the last cup game under the lights at Upton Park, and we scored in the last seconds.
"We had injuries and we overcame all of that. I think it will go down as one of the greatest games and greatest nights in the history of this club."
The Hammers are, of course, leaving Upton Park at the end of the season but the famous old ground crackled with an atmosphere it will surely be impossible to recreate at the Olympic Stadium.
The match was worthy of the occasion, as well. Joey O'Brien and Dimitri Payet hit the woodwork for West Ham, Philippe Coutinho did the same for Liverpool, all in the first half.
Michail Antonio's far-post volley separated the sides at the break, but just three minutes into the second half Coutinho drilled a cheeky free-kick under West Ham's defensive wall to level.
Chances then came and went for both sides. Christian Benteke drove stright at Darren Randolph when clean through, and fit-again sub Daniel Sturridge fired narrowly over, while for the Hammers' Enner Valencia's header was just off target.
But with players from both sides starting to wonder which side to place their penalties, West Ham were awarded a soft free-kick for Lucas' foul on Valencia.
Payet floated it in and Ogbonna crashed in a powerful header to send three sides of Upton Park into delirium.
The Hammers are to offer French playmaker Payet a new contract just seven months after signing him, amid reports of a bid of ?38million from an unnamed Chinese club for him.
But Bilic added: "I'll say it again. We are a club moving forward and the most important moves are on the pitch. We must do everything we can to keep our best players, and he is our best player.
"He's happy here and very soon we will sort out his situation."
It must have been an uncomfortable evening to be a losing manager, not least one who had had his appendix removed just three days earlier like Jurgen Klopp.
The Anfield chief picked a youthful side again and they were desperately unlucky to come up short.
"I thought they could play like that so I'm not surprised," said the German. "But the only reason we were here is to win the game and get to the next round.
"We did a lot of things really good, we played the game in the right direction. But the first real chance went to West Ham.
"Our goal was great, a high-quality goal from Coutinho. Then still we did well, created chances and put up a big fight.
"Then they got a free-kick, without a foul, and we concede a goal. So now we go home."