The Blues had their goalkeeper sent off after only five minutes.

Ruben Amorim's Manchester United ended an eventful encounter with a much-needed 2-1 victory over Chelsea as Robert Sanchez's early red card proved more costly than goal-scorer Casemiro's sending-off.

Pressure has been mounting on the Red Devils boss after the club's worst top-flight season in 51 years was compounded by a sluggish start to the new campaign.

Under-fire Amorim got the response he needed to United's meek Manchester derby defeat, with Bruno Fernandes and Casemiro scoring in a chaotic first half bookended by red cards before the hosts saw off a late Chelsea charge sparked by Trevoh Chalobah's header.

It was an action-packed match played in challenging conditions at Old Trafford, where the hosts capitalised on Chelsea goalkeeper Sanchez's mistimed tackle five minutes into the game.

Fernandes marked his 200th Premier League appearance with his 100th goal for United and Casemiro nodded Amorim's men further ahead before needlessly picking up a second yellow card in first-half stoppage time.

United fans goaded Chelsea substitute Alejandro Garnacho on his return to Old Trafford, with Chalobah's header making for a nervy ending but failing to inspire a Chelsea comeback.

The relief was palpable at the end of a match that started with the visitors shooting themselves in the foot.

Sanchez had denied an early Bryan Mbeumo effort and his next attempt to stop the lively summer signing led to an early bath.

Benjamin Sesko's brilliant flick-on put Mbeumo in behind Chelsea's backline, with the keeper rashly bringing down the forward with a high tackle as last man. Referee Peter Bankes had no choice but to brandish a red card.

Enzo Maresca brought on goalkeeper Filip Jorgensen for Estevao and, before play resumed, decided to move to a back five by introducing Tosin Adarabioyo. Pedro Neto was sacrificed and screamed in frustration.

The match became an attack-versus-defence exercise, but patient United found a way through in the 14th minute.

Noussair Mazraoui did well to get over a first-time cross from the right and Patrick Dorgu headed the ball back across goal for Fernandes to prod past Jorgensen. The goal was awarded after a lengthy VAR check for offside.

Mbeumo bent a shot narrowly wide from the edge of the box as United sought a quickfire second and Maresca reacted by taking off star man Cole Palmer in the 20th minute to the delight of the Old Trafford faithful.

Casemiro saw a goal ruled out after Amad Diallo failed to keep the ball in play before crossing, but the Brazil midfielder would not be denied for long.

Chelsea failed to deal with danger and Luke Shaw bravely attacked a high ball, with the ball going off Harry Maguire and on to Casemiro to nod past Jorgensen in the 37th minute.

Maresca's visitors looked rattled as United showed the aggression Amorim had called for in the build-up, albeit Casemiro took it too far five minutes into first-half added time.

The veteran had already been booked and his overzealous challenge on Andrey Santos led referee Bankes to show him a second yellow. Amorim walked away shaking his head.

Manuel Ugarte replaced Sesko for a second half that began with pools of surface water making play difficult.

Garnacho received an earful from the Stretford End as he warmed up in front of them, but he would not step on to the field as Maresca looked to other players after Wesley Fofana saw a goal from a corner ruled out for offside.

United made changes of their own as the sought to keep Chelsea at bay, but Amorim's men rarely do things the easy way.

The tired-looking hosts were caught cold from a quickly-taken corner as Reece James swung in a fantastic cross for an unmarshalled Chalobah to head past Altay Bayindir in the 80th minute.

Fernandes saw a shot well saved and Bayindir survived a late scare after pushing a James cross back into the danger zone, with the final whistle bringing United's second win of the season.

Manchester United hold on for overdue win as Chelsea rue Robert Sanchez red card