Manchester United returned to Premier League action against Chelsea at Stamford Bridge; here are five things we learned.

Manchester United had a dreadful start at Stamford Bridge on Thursday night.

Chelsea seized the lead within five minutes through Conor Gallagher, and the Blues made it 2-0 not long after.

This left United with a mountain to climb, and Alejandro Garnacho took the first steps up it.

Bruno Fernandes then equalized in the 38th minute, converting Diogo Dalot’s wonderful cross to make it 2-2.

Garnacho then completed the comeback, meeting Antony’s wonderful cross to make the score 3-2.

Chelsea then scored twice in added time to secure three points in United’s 4-3 loss.

Here are five lessons we learned.

Alejandro Garnacho proves himself as the key man.

Alejandro Garnacho, 19, was a strong player for United, as he has been throughout the season.

Garnacho, who was moved back to the left after Marcus Rashford was substituted, scored United’s opening goal to kickstart the comeback.

He was quite cool about it, fighting off pressure from the Chelsea defender and beating the keeper well. He also did an excellent job finishing off Antony’s perfect cross for United’s third goal.

He also contributed to United’s second goal, setting up Dalot for a cross.

He has immediately emerged as a top player this season.

Antony is finally revealing why he got signed.

After a season and a half of challenges, Antony has just demonstrated why Erik ten Hag was so eager to sign him.

For the first goal, he did an excellent job of keeping an errand Fernandes pass in play, which led to Moises Caicedo’s error.

Then he had a couple magical moments, beating numerous defenders on one or two occasions.

The best thing he accomplished was set up Garnacho for his second goal. Outside of the boot pass, which landed exactly in Antony’s path.

Antony put up an outstanding performance in this game, more than making up for his early penalty blunder.

For United, Casemiro appears to be far from his best.

Casemiro was one player who appeared completely out of sync throughout the game, struggling to get close to any Chelsea player.

His lack of work rate, along with his poor recovery in transition (he basically jogged), allowed vast openings for Chelsea to exploit.

He was a poor tackler who frequently went to the ground when he shouldn’t have, creating even more room for Chelsea to exploit.

A player who appears to be nearing the end of his United career; time to locate a top-tier replacement.

Erik ten Hag’s defensive woes worsen

Lisandro Martinez and Victor Lindelof both suffered injuries prior to this game, which was some startling news.

Following the game, the centre-back injury list has been doubled, with both Jonny Evans and Raphael Varane forced off due to injuries.

This leaves Ten Hag with only Harry Maguire and Willy Kambwala, one of whom has lately returned from injury.

Another topic that has to be handled seriously this summer.

The Champions League dream is over.

Coming into this game, United just had one goal in mind: win and keep their Champions League hopes alive.

This, however, proved to be too much to expect, as United squandered all three points in extra time, with Cole Palmer scoring first from the penalty spot, then via a tremendous deflection.

An great game, but Ten Hag will be furious because he has had to watch his team’s incredible work undone in the space of two minutes, a real momentum killer for United ahead of their match against Liverpool.