Sheffield United claimed a Premier League scalp as they prevailed 5-4 in a Capital One Cup second round penalty shoot-out with West Ham United.
The Upton Park contest had ended 1-1 after 120 minutes, with Diafra Sako edging the hosts in front, only to see Winston Reid put through his own net to restore parity.
West Ham fans taunted their Sheffield United counterparts with chants about Carlos Tevez - only to see their latest big-money signing miss the decisive penalty.
This was the first meeting between the two sides since the Blades were relegated in 2007, largely thanks to Tevez's goals at West Ham - only for a legal wrangle over the Argentina international's ownership leading to the Hammers paying out almost £30million in compensation.
There are now two divisions separating the clubs but it is Sheffield United who progress into the third round after Enner Valencia, a £14million signing from Pachuca, was the only player to miss his spot-kick.
Sakho was quiet but managed to put the Premier League side ahead with a well-taken first-half header, only for Reid - captain for the evening - to score an unfortunate second-half own goal, with few chances created by either side as the game meandered into extra time and eventually to penalties.
Both sides converted their opening four spot-kicks before Valencia, who had wasted a couple of good chances during the night, saw his low effort saved by the impressive Mark Howard.
Blades' skipper Michael Doyle then stepped up to seal the win for Nigel Clough's side - who will see the result as a small piece of revenge for the whole Tevez saga.
Debuts
Sakho, as well as fellow summer arrivals Diego Poyet and Valencia, were handed full debuts, as was 17-year-old defender Reece Burke.
Ravel Morrison was also given his maiden outing of the season, with groin surgery and assault charges both keeping the England Under-21 international away from first-team duties to date.
West Ham started on the front-foot but could not muster a clear-cut chance, with Valencia and Ricardo Vaz Te getting in each other's way as they looked to attack Guy Demel's cross.
The visitors were determined not to be soaking up pressure all evening and could have taken the lead had Marc McNulty made better contact with Jose Baxter's through ball.
Instead his effort was blocked for a corner, which Craig Alcock steered wide of Jussi Jaaskelainen's post as he met the set-piece unchallenged.
Big-money signing Valencia spurned the best opening of the first half as he could only shoot straight at Howard, having been played through on goal by a slide-rule Mohamed Diame pass.
Howard continued to keep Clough's side in the game, first pushing away a Morrison free-kick before Burke's volley from the resulting corner was scooped clear by the former Arsenal youngster.
If Valencia's radar was askew, fellow forward Sakho's was in perfect working order as the new arrival from Metz rose to flick home Burke's long-ball into the box to put the Hammers ahead.
Another defence-splitting pass from Diame moments later saw Demel break into the box and look to feed Valencia, but his ball to the back post zipped past the Ecuador international.
The second half began with neither side seemingly wanting to take the game by the scruff of the neck, but the League One side were level in fortuitous circumstances.
A low cross from the left eluded McNulty and hit Reid, with Jaaskelainen wrong-footed and the ball rolling into the unguarded net to level the tie.
Target
McNulty came close to turning the game on its head as the hour-mark approached but he could not find the target as Bob Harris once again crossed from the left.
Downing was introduced from the bench in place of goalscorer Sakho and his low corner was flicked wide by Reid as the New Zealand international looked to atone for his earlier own goal.
With Downing playing from the right, West Ham were instantly offering more of a threat and the England winger's deep cross on 65 minutes was acrobatically volleyed at goal by Vaz Te, only to be blocked behind for a corner.
The chances became more limited as the half progressed, with Allardyce turning to Mauro Zarate with a little over 10 minutes remaining as Vaz Te made way.
Downing came close with a thundering effort from outside the box, but Howard again proved up to the task as he tipped behind for a corner.
Zarate was the next to test Howard, this time stinging the palms of the 27-year-old with no team-mate on hand to feed on the scraps.
Extra-time became an inevitability, with a smattering of jeers from the home fans when Linington blew for the end of 90 minutes.
There was a scare for the home side as a Jay McEveley shot squirmed through Jaaskelainen's grip to be cleared off the line by substitute Mark Noble in the opening period of extra-time, but the game had lost all of its edge by that point.
The final 15 minutes saw Sheffield United fall deeper and deeper into their own half, with West Ham peppering the defence with long-range shots, all of which were blocked or cleared.
The visitors hung on to take the game to the lottery of penalties and, with both sides having perfect records at 4-4, Valencia failed to convert and Doyle showed the character to step up and take his side through.