League One side Lincoln City shocked Sheffield United 3-2 on penalties to oust the Premier League club from the Carabao Cup in the second round at Bramall Lane.
Captain John Egan missed the Blades' final penalty of the shootout after strikers Louie Marsh and Benie Traore had their spot-kicks saved by 6ft 6in goalkeeper Lukas Jensen, sending the Imps through in front of the ecstatic away end.
"It's the best feeling," said Jensen, who did not make an appearance during a four-year spell at Burnley before joining Lincoln in June.
"I don't think you can describe it - you have to be in the moment. All the feelings and emotions came out.
"Big credit to my goalkeeper coach. I think they nicked my bottle, so I couldn't see where they were going to shoot.
"To do it in front of all our fans on that side is an amazing feeling - to have 3,000 fans cheering and celebrating with us after the game. All the credit should go to the team."
The shootout victory came after the sides were goalless after 90 minutes and rewarded an impressively organised defensive display from Mark Kennedy's side, who said they would not fear opponents two divisions above them and were rarely troubled despite the hosts dominating possession.
Unbeaten in five games in all competitions as part of a run that had moved them two points off the top of League One, Lincoln showed their confidence by producing the only accurate attempt of the first half through full debutant Alex Mitchell, whose effort was gathered by Adam Davies.
United manager Paul Heckingbottom saw his players command 75% of the ball in the first half but struggle to create danger, Ollie Norwood resorting to an audacious long-range effort that cleared the crossbar.
Cameron Archer - making his debut after signing from Aston Villa for £18m - twice called Jensen into action after half-time as part of an energetic display that stood out in a flat United performance which leaves them still seeking a first win after four games of the season.
Heckingbottom made changes after the break, sending on two attackers in summer singing Traore and 19-year-old Marsh in place of Oli McBurnie and winger Andre Brooks.
Three 20-year-olds - Femi Seriki, Jili Buyabu and William Osula - also came on within 20 minutes of the restart in an attempt to inject some much-needed energy after Teddy Bishop almost broke through for the visitors.
Bishop, who had his penalty saved by Davies, had already threatened following his half-time introduction in place of Ben House, but Egan should have scored with a free header as penalties loomed, then sent his penalty over the crossbar.
"I felt good, and then after their second penalty I felt even better," said 24-year-old Dane Jensen. "It all worked out.
"I must have done something right to put the pressure on [Egan] to put it over the bar. He tried to smash it and it didn't work.
"When I saw it went over, I turned around and celebrated with all the fans. To see that many here is unbelievable."
United return to Premier League action on Saturday at home to Everton, while Lincoln visit 17th-placed Bristol Rovers on the same day in the third tier.
Sheffield United assistant boss Stuart McCall told BBC Radio Sheffield: "No excuses - it was a flat performance. It would be easy to say it was on the back of Sunday and having a full house against Man City. We discussed that before the game - we have to make our own atmosphere.
"Lincoln brought a good contingent, filled their end and got behind their side. It's not to take anything away from Lincoln. They were good and you've got to give them credit. They defended really well in their shape and were hard to break down but we've got to be creating more than that.
"The manager summed it up at the end - we were bored watching it. That's how we don't want our teams to play; we want to be on the front foot, creating chances and getting balls in the box."
Lincoln City boss Mark Kennedy told BBC Radio Lincolnshire: "The lads were outstanding. The discipline was incredible, to have the ability to be coachable and go and execute it. On the ball in transitions, we looked a real danger. Admittedly, both keepers had a quiet game but we had some really good 'nearly' moments.
"I don't think anybody could argue with us taking Sheffield United to penalties. I'm super, super impressed but not surprised - I see it most weeks. When you play in League One, one thing you don't get with a lot of teams is consistency. We are incredibly consistent in who we are and what we do. I was really confident of that happening tonight.
"If we had come here and lost 3-0, would I have been surprised? No, because they're a Premier League team. But am I really shocked that we've got a clean sheet, taken a team to penalties and won? No, because I see it every day with the group. The guys should be really proud of each other. Players, staff fans - everybody should be really proud to be connected with Lincoln tonight."