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.MATCH REPORT | Martinelli stars as Premier League leaders Arsenal crush Everton to go 5 points clearIn 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. Fifth round Burnley 1 (Roberts 90) Fleetwood 0Manchester United 3 (Aguerd 77-og, Garnacho 90, Fred 90+5) West Ham 1 (Benrahma 54)Sheffield United 1 (Ndiaye 79) Tottenham 0Southampton 1 (Caleta-Car 65) Grimsby 2 (Holohan 45+1-pen, 50-pen) Played on Tuesday: Stoke 0 Brighton 1 (Ferguson 30)Leicester 1 (Iheanacho 67) Blackburn 2 (Dolan 33, Szmodics 52)Fulham 2 (Palhinha 21, Solomon 56) Leeds 0Bristol City 0 Manchester City 3 (Foden 7, 74, De Bruyne 81)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