Manchester United capitalised on Robert Sanchez's fifth-minute red card to secure a crucial victory over Chelsea in torrential rain at Old Trafford.

The first match in Premier League history to see two or more goals, red cards and substitutions in the first half was settled by goals from United skipper Bruno Fernandes and Casemiro, who was the other player sent off before the break.

It was Sanchez's dismissal that set the course of the game though.

The Spain international raced from his goal to meet Bryan Mbeumo as the striker ran beyond the Chelsea defence.

Sanchez then upended the forward outside his area rather than allow him past to tap the ball into an empty net.

Enzo Maresca's response to the red card was to take off both Pedro Neto and Estevao Willian and, as Cole Palmer had to be replaced after suffering a recurrence of a groin injury, Chelsea had lost three attacking players in the space of 20 minutes.

Trevor Chalobah pulled one back for Chelsea with a header 10 minutes from time but United kept their nerves at bay to make it to the final whistle with their lead intact.

The victory was United's second of the season and came in front of minority owner Sir Jim Ratcliffe, who gave head coach Ruben Amorim assurances over his future 48 hours earlier.

It also means Chelsea have still not won at Old Trafford since 2013, when Sir Alex Ferguson was United manager.

Man Utd analysis: Winning all that matters just now

As strange as it may seem, United have now won three of their past four Premier League home games, with their single blemish coming against Arsenal on the opening day of the season.

Strangely though, two of those victories have come after the visiting team had their goalkeeper sent off before half-time when the game was still goalless.

Just as against Aston Villa on the final day of last term, United took maximum advantage.

However, while the Villa victory was largely academic, this time the three points were absolutely crucial.

It is not just that the win sent Amorim's side into the top half of the table - they are only two points off the top four - but it injected some confidence into a club that seemed to be existing more in hope than expectation of a drastic improvement, for all their bold words recently.

Fernandes underlined the importance of victory after he had a shot superbly saved by replacement Chelsea goalkeeper Filip Jorgensen a couple of minutes before the end, roaring at the Stretford End to make more noise.

The Portugal playmaker was on the edge of his seat in the final seconds of injury time, at which point he had been replaced by Kobbie Mainoo.

While the shape of the game was changed by the red cards - Casemiro's, for hauling back Andrey Santos to get a second yellow just before half-time was particularly silly given the state of the game - and the awful conditions that had water splashing on the pitch at start of the second period - this was not about tactical analysis anyway.

As Amorim said in his programme notes, it was time for actions and his team delivered.

Now they must go to Brentford and try to win successive Premier League games for the first time under the former Sporting boss.

Chelsea analysis: Same old, same old at Old Trafford

This chaotic collapse was so typically Chelsea at Old Trafford.

The Blues have not won since 2013 at this stadium and - despite United being a declining superpower - they keep finding innovative ways to lose at this ground.

On this occasion, the defeat came because of a calamitous 45 minutes.

It began unravelling after Sanchez's red card, which was the club's earliest ever in the Premier League, and came after just four minutes and one second. That moment reflected poorly on both the keeper and his defence for leaving the space in behind.

Manager Maresca decided to take off attackers Estevao Willian and Neto for a new goalkeeper Filip Jorgensen and defender Tosin Adarabioyo. It appeared as if the Italian boss was trying to stay in the game, with the remaining 10 players featuring a back five and goalkeeper.

However, the plan backfired as within nine minutes Bruno Fernandes scored and a further seven minutes later star forward Cole Palmer came off with a flare up of a previous groin injury.

Palmer was replaced by midfielder Andrey Santos after 20 minutes and five seconds, which is the earliest any Premier League team has made three substitutions. The England forward went straight down the tunnel for treatment before coming back out to watch the game with an ice pack on the affected area.

Casemiro scored late in the half and was then sent off just before the interval but -despite Chalobah's late headed goal - Chelsea could not salvage a point.

Losing Palmer is a big concern following a difficult week featuring a draw at Brentford and defeat at Bayern Munich. (BBC)