Reading bowed out of the Emirates FA Cup in heartbreaking fashion, with Premier League Sheffield United striking in extra time to take a 2-1 win against the Royals in the Fifth Round.
David McGoldrick headed the visitors in front within the first two minutes in RG2, but George Pușcaș struck back from the spot before half-time to take the tie to an extra half-hour.
Reading had been dominating, but a break in extra time saw Billy Sharp able to capitalise and send the visitors through to the last eight of the FA Cup.
Reading lined up unchanged from their weekend win over Barnsley at Madejski Stadium, while the Blades took part in their first match for more than a week after their Premier League fixture at the weekend was postponed, due to Aston Villa's involvement in the Carabao Cup Final.
And the visitors put themselves in front with only 82 seconds on the clock in the first attack of the game. Ben Osborn found space on the left to hang up a cross into the area, with McGoldrick on hand to head into the ground and into the roof of the net. The Premier League side had the upper hand almost immediately.
Bruised but unfazed, Reading were able to then settle into the match, keeping control of the ball as they looked to calm themselves down after going behind so early. Conceding early did not hamper the vocal support from Club 1871 either, with Madejski Stadium a cauldron of noise in this FA Cup tie.
Reading had to work hard for every opportunity against Chris Wilder's side, but put a neat passing move together in midfield before spreading play to Yakou Méïté.
He was able to cut into shooting range 25 yards out on his favoured left foot, firing a bullet of an effort towards the top corner and forcing a save straight out of the top drawer from Dean Henderson in the Blades goal - diving high to his right to stop the ball taking the net from its foundations.
The Royals had control of the game by now, forcing the Blades back and having the unenviable task of playing through a defence that has conceded the second-fewest goals in the Premier League all season.
The visitors hadn't threatened Rafael's goal after opening the scoring, but a dangerous corner near the half-hour mark found John Egan's head at the near post, nestling on the roof of the net.
Mark Bowen's men were doing all they could to pen the Blades in, work the channels and pile on the pressure to equalise before the break, but they couldn't quite find the opening they needed.
Andy Rinomhota showed tenacity in midfield to turn his marker and try to slide a ball through to George Pușcaș on the run, but it had a bit too much speed and Henderson was able to watch the ball out for a goal kick.
But three minutes before the break, Reading had a lifeline from the spot. George Baldock nudged Rinomhota in the box when he went up for a header, and Kevin Friend did not hesitate in pointing to the spot.
Pușcaș stood over it, with Madejski Stadium waiting with bated breath for the whistle to blow. Henderson guessed the right way, but the Royals striker buried it in the bottom corner to deservedly put Reading level in the cup tie.
The outcome of this match was anyone's guess as the half-time whistle blew. Game on at the Madejski.
Half-time | Reading 1-1 Sheffield United
Play restarted with the same intensity with which the first half had ended, with both teams jockeying for the ball in a lively encounter.
Reading forayed forward with Pușcaș on the right, linking up well with Rinomhota before the striker sent a ball into the area. Olise was the recipient at the far post, controlling and firing wide from 15 yards or so.
Andy Yiadom showed fantastic footwork to dance his way between three Blades markers in the defensive third, showing the Royals were more than up for the fight against their high-flying Premier League opponents.
The Royals pushed forward again, with Méïté doing brilliantly to beat Egan to a header in the attacking third, with Yiadom rather lashing at his strike, though, and didn't trouble Henderson with the ball sailing over the bar.
Reading had the better of it in the early stages of the second half. Ovie Ejaria showed deft footwork to set the Royals on another attack, with the ball whipped into the area once more. Pușcaș was bundled over in the box, prompting appeals for another Royals penalty - waved away this time.
The Royals were on the warpath to try and put themselves ahead. John Swift twisted and turned to work himself into enough space to loft a ball over the Blades defence. Méïté did all he could to run onto it in the area, but Henderson scrambled off his line to make it just before the Ivorian.
Sheffield United rarely troubled Reading's goal until midway through the second half, when a cross from Osborn found McGoldrick's head once more. He couldn't guide this effort on target, however, with Rafael watching it over the crossbar.
The tie became stretched as time ticked on, with the match taking a turn to become increasingly end-to-end with both teams in search of a winner and that all-important Quarter-Final place.
Luke Freeman pounced on a loose ball 30 yards from goal and tried a speculative drive for the Blades, with Rafael having to be alert and dive to his left to parry.
The noise level continued to be high on the night at Madejski Stadium in an open, expansive, proper FA Cup tie. Time was running out to find a winner, but extra time and penalties were available if needed.
A Swift ball into the box troubled Henderson to the point that he had to parry away for a corner, with Olise over the set piece. His initial ball was blocked by sub, Oliver McBurnie, with play recycled and the teenager trying to put another cross in, with the Blades watching it behind and out of play.
Just two minutes were added at the end of the 90, but Reading had to gear up for an extra 30 as the teams could not be separated by the final whistle.
After 90 minutes | Reading 1-1 Sheffield United
Extra time would see the players tested to their physical and footballing limits, and Reading started brightly in the added half-hour.
The Royals moved forward with purpose, and Obita put a dangerous cross into the area but Henderson was able to claim in the air.
Bowen made a double substitution shortly afterwards to inject some freshness into the tired Reading legs, with Ayub Masika and Pelé introduced for Ejaria and Olise respectively.
Reading were having the better of the action once again, with a spell of pressure finishing with Rinomhota cleverly chipping his way into the box. He went to shoot left-footed, but the ball bounced wide of Henderson's post.
There was to be a sting in the tail before the end of the first half of extra time, excruciatingly for the Royals.
Freeman was able to get into space on the left of the box, who hung up a cross to the far post for Sharp to head in and put the Blades in front once again, totally against the run of play.
Reading had 15 minutes to get level again.
Half-time (Extra-time) | Reading 1-2 Sheffield United
Sam Baldock and Garath McCleary were both brought on for the final 15 minutes at the Madejski, with this Emirates FA Cup tie going the distance.
The Blades did all they could to run the clock down as much as possible, having taken the advantage again in the match.
Reading continued to fight valiantly on the pitch, with the visitors keeping men behind the ball and breaking up play.
Obita tried his luck from range with six minutes left on the clock, with the Royals now piling forward in search of another equaliser.
McCleary then burst into the area and played across goal, agonisingly out of reach of the blue and white shirts in the box and United could clear their lines once more.
Reading got forward yet again with Masika showing a burst of pace, finding McCleary, who then played to Pelé, whose low drive forced Henderson into another save.
Pelé soon tried his luck again when Morrison controlled well outside the box, laying off to the midfielder, who dragged a matter of inches wide.
A massive effort all round over two hours of football from the Royals, but it wasn't to be on the night.
After Extra Time | Reading 1-2 Sheffield United
Reading: Rafael, Yiadom, Morrison (c), Miazga, Obita, Rinomhota (Baldock 106), Swift, Ejaria (Pelé 98), Olise (Masika 98), Méïté (McCleary 106), Pușcaș.
Unused subs: Walker, Moore, Blackett.
Goals: Pușcaș (43 PEN)
Sheffield United: Henderson, Baldock, O'Connell, Egan (c), Basham, Osborn, Lundstram, Freeman (Retsos 106), Berge (Robinson 99), McGoldrick (Sharp 79), Mousset (McBurnie 61).
Unused subs: Verrips, Jagielka, Retsos, Zivkovic.
Goals: McGoldrick (2), Sharp (105+1)
Referee: Kevin Friend
Attendance: 15,129 (2,086 away)