Harry Maguire’s thumping header secured FA Cup holders Manchester United a controversial late 2-1 comeback win against his former club Leicester and returning favourite Ruud van Nistelrooy.

The former Leicester defender was offside but there is no VAR at this stage of the FA Cup.

Van Nistelrooy rejoined the club in the summer as one of Erik ten Hag’s assistants and looked set to haunt his former employers on his first visit to Old Trafford since Ruben Amorim let him go.

Bobby De Cordova-Reid put Leicester ahead against lifeless United, who were booed off at the break but found a way past the Premier League strugglers in the second half.

Alejandro Garnacho was introduced at half-time and helped change the tie, seeing an effort brilliantly cleared off the line by Caleb Okoli before sending in a cross that ended with fellow substitute Joshua Zirkzee tapping in.

The fourth-round tie was heading towards extra time as stoppage time ebbed away, only for Bruno Fernandes to swing in a free-kick powered home by Maguire.

It was a breathless end to what had been a forgettable encounter.

United’s players warmed up in special tops showing support for popular team-mate Lisandro Martinez, who suffered cruciate ligament damage in Sunday’s home loss to Crystal Palace.

January signing Patrick Dorgu replaced him in the line-up and made his debut at right wing-back, rather than taking up a more familiar left-sided role, showing some bright moments in a cagey, shot-shy first half.

Jordan Ayew saw an early 25-yard attempt held by Andre Onana and it took 20 minutes for United to muster a shot, with Amad Diallo’s effort blocked for a corner that ended up with a Dorgu drive over.

United lacked quality and creativity as grumbles of discontent grew in stands that began to empty three minutes before the break.

Manuel Ugarte was all too easily dispossessed and Boubakary Soumare poked onto Bilal El Khannouss, whose cutback was met by a first-time Wilfred Ndidi strike.

Onana made a save with his feet but De Cordova-Reid quickly reacted to head home from three yards.

Leicester fans were loving life in the away end at Old Trafford, where loud boos from the locals greeted the half-time whistle.

Garnacho replaced Dorgu at the break and added more attacking impetus, but Leicester were still getting joy and El Khannouss dragged across goal after being allowed to run forward.

Noussair Mazraoui sent a long-range attempt wide as United looked for a moment of magic, with home fans beginning to chant “attack, attack, attack” as Zirkzee entered the fold and their side went close.

Ugarte slipped Garnacho through on goal in front of the Stretford End, which was ready to burst into life as a block took the ball over goalkeeper Mads Hermansen.

But Okoli got back to stretch and superbly clear off the line and onto the bar, with the Foxes defender’s delight at his intervention clear.

That chance breathed new hope into the home supporters and the 68th minute brought a leveller.

Rasmus Hojlund saw a fine flick blocked after Garnacho’s good work and low cross from the left, but the ball fell kindly for Zirkzee to apply a simple finish.

The relief was palpable and Garnacho looked most likely to put United ahead, although his decision to shoot rather than cross infuriated Hojlund in the 79th minute.

United pushed and the Argentina international saw a thumping attempt held after Ugarte’s challenge on Harry Winks drew gasps but just a booking.

And just as fans braced themselves for extra time a free-kick ended the tie.

Fernandes sent a ball over to Maguire, who was able to power a header home without the VAR ruling the goal off for offside.