Alejandro Garnacho and Fred struck late as Manchester United came from behind to beat West Ham 3-1 in the FA Cup on Wednesday but Tottenham were dumped out by Championship side Sheffield United.

In the night'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.

West Ham had the better chances in the first half but looked blunt in attack without the cup-tied Danny Ings.

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 swapped 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.

United finally drew level five minutes later when Fernandes sent in a corner and Nayef Aguerd headed past Alphonse Areola and 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 90th-minute effort to edge United ahead followed by a stoppage-time strike by Fred to add gloss to the scoreline.

- 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 Sheffield United to a 1-0 fifth-round win at Bramall Lane.

After starting Harry Kane on the bench, they fell behind to Ndiaye's 79th-minute opener and could not find a way back.

New Southampton manager Ruben Selles made nine changes to his team for the home tie against League Two Grimsby.

The visitors went 1-0 ahead just before half-time through Gavan Holohan's penalty and doubled their lead five minutes into the second half when Holohan converted his second spot-kick of the evening.

Relegation-threatened Southampton halved the deficit in the 65th minute when Duje Caleta-Car atoned for conceding the second penalty by volleying in a corner from substitute James Ward-Prowse.

Southampton substitute Theo Walcott thought he had equalised 10 minutes from time, only to be deemed offside following a VAR review.

Championship leaders Burnley needed a 90th-minute goal from Connor Roberts to edge out the 10 men of League One Fleetwood 1-0 and advance to the quarter-finals of the FA Cup for the first time in 20 years.

In Tuesday's matches, Manchester City reached the quarter-finals with a 3-0 win against Bristol City 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.