London - Alejandro Garnacho and Fred struck late as Manchester United came from behind to beat West Ham 3-1 and reach the FA Cup quarter-finals on Wednesday but Tottenham were stunned by Championship side Sheffield United.
In the evening's other fifth-round ties, fourth-tier Grimsby embarrassed Premier League strugglers Southampton 2-1 and Burnley beat 10-man Fleetwood 1-0.
Manchester United, who made six changes to the team that started Sunday's League Cup final win against Newcastle, lacked fluency in front of an expectant Old Trafford crowd.
United goalkeeper David de Gea thwarted Michail Antonio when the West Ham forward bore down on goal midway through the opening period and Emerson Palmieri flashed an inviting ball across the box.
United manager Erik ten Hag brought on Casemiro for Scott McTominay at half-time but the home side remained sluggish.
Said Benrahma made them pay in the 54th minute, rifling the ball past De Gea after the home defenders stopped, thinking the ball had gone out for a throw-in.
The goal prompted Ten Hag to introduce top-scorer Marcus Rashford but Antonio had a glorious chance to double West Ham's lead, only to be denied again by De Gea.
Casemiro had the ball in the net in the 72nd minute but his header from a Bruno Fernandes free-kick was ruled out for offside following a VAR review.
United finally drew level five minutes later when Fernandes sent in a corner and Nayef Aguerd headed into his own goal.
The home side -- still on a high after ending their six-year trophy drought at the weekend -- poured forward in search of a winner.
They got their reward when Argentine teenager Garnacho produced a superb right-footed curler in the 90th minute to edge United ahead followed by a stoppage-time strike by Fred.
"The best teams never stop believing," United captain Harry Maguire told ITV. "I am not saying we are one of the best teams yet.
"We have a lot to do but we are getting there, we are taking steps forward... It felt like the Stretford End was sucking the goal in at the end there." - Spurs dumped out - Tottenham were dumped out of the FA Cup by Championship opposition for the second year in a row after Iliman Ndiaye fired promotion-chasing Sheffield United to a 1-0 win at Bramall Lane.
Spurs, who started Harry Kane on the bench, conceded in the 79th minute and could not find a way back, with Kane heading an Ivan Perisic cross over deep into injury time.
Tottenham assistant manager Cristian Stellini, standing in for Antonio Conte, who is recovering from gallbladder surgery, apologised to the fans.
"If you don't win a game like this it's because something was not perfect and today our energy was not enough to put the opponent in a great difficulty," he told the BBC.
New Southampton manager Ruben Selles made nine changes to his team for the home tie against League Two Grimsby.
Two Gavan Holohan penalties either side of half-time put the visitors 2-0 up and although Duje Caleta-Car halved the deficit, Grimsby held on.
"We turned up, hoping for a miracle and to be in the quarter-final is incredible," Grimsby manager Paul Hurst told ITV. "It is just a fantastic day, we have gone down in the history books." Championship leaders Burnley needed a 90th-minute goal from Connor Roberts to edge out the 10 men of League One Fleetwood.
In Tuesday's matches, Manchester City beat Bristol City 3-0 while 2021 winners Leicester suffered a shock 2-1 defeat against second-tier Blackburn.
Fulham beat Premier League strugglers Leeds 2-0 and Brighton won 1-0 at Championship side Stoke.
City will take on Burnley in the quarter-finals, with Manchester United hosting Fulham. Grimsby travel to Brighton while Sheffield United host Blackburn. - John Weaver / AFP