Manchester United dropped a defensive disasterclass in the Champions League on Wednesday.Despite having opened their European campaign with impressive wins over Paris Saint-Germain and RB Leipzig, it seems as though their poor Premier League form is rubbing off elsewhere.That's because, mere days after their drab 1-0 defeat to Arsenal, the Red Devils flew back to Old Trafford without a single point upon losing 2-1 away to Istanbul Basaksehir.

United embarrassed by Istanbul

While the Turkish side are by no means a pushover, they stand out as by far the weakest team in United's group and it was two instances of terrible defending that cost them on the night.

The first strike saw Demba Ba running clean through on goal from the halfway line - where have we heard that before? - with United inexplicably leaving him unmarked after winning a corner.

Quite why Nemanja Matic decided that 'marking' him by standing within merely 15 yards is beyond us, but it made for the sort of goal you'd expect to see in Sunday League or from under-10s.

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United's defensive woes

By comparison, the second goal was a little less egregious, but screenshots of three United players basically marking each other while Edin Visca wound up to score is rather humiliating.

And let's face it, United fans, this is far from the first time that dreadful defending has proved costly during Ole Gunnar Solskjaer's era and we've decided to hone in on that weakness.

In fact, we've selected an unlucky 13 of defensive errors that have blighted United since Jose Mourinho was sacked in December 2018 - and the results are pretty horrendous.

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Man Utd's 13 worst mistakes

Pessimists might call it a gruesome post-mortem of the defeat in Turkey, but optimists will like to think it shows the only way is up going into the weekend's league clash with Everton.

Either way, defensive purists look away and check out the instances of madness down below:

1. Chris Smalling and Phil Jones disaster vs Wolves

It's like watching a car crash in slow motion. The ball eventually wangled its way past the line after an absolute pile up between Jones, Smalling and David de Gea in their own six-yard box.

We can't decide what's more amusing: Smalling stumbling into his own goalkeeper and being left on all fours or yet another classic facial expression from Jones moments before disaster.

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2. Carved upon by Huddersfield Town

Let's not beat around the bush, the Huddersfield side of 2018/19 are one of the worst the Premier League has ever seen and they entered this game having avoided defeat just twice in their last 23 fixtures.

So imagine the shock as United inexplicably manage to concede from their own corner with Jonas Lössl launching the ball down the pitch in one go and leaving Luke Shaw to make a ballet pose.

3. Jones clanger vs Sheffield United

We'll happily admit that we rate Jones higher than a lot of supporters, but the guy doesn't help himself at times and he was substituted at half-time during the 3-3 draw at Bramall Lane.

It probably had something to do with his role in the Blades' opener with Jones getting bullied out of possession way too easily by Lys Mousset after a long ball over the top.

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4. Williams, Jones and Perreira mess vs Man City

If there's any consolation for United here, it's that no one player is entirely at fault and Andreas Pereira might be the least guilty party despite eventually putting it past his own goalkeeper.

Besides, the writing was on the wall by the time Brandon Williams completely botched what could have been an attacking-halting tackle and Kevin De Bruyne folded Jones like a deckchair.

5. David de Gea howler vs Watford

Credit to De Gea for turning his form around this season, but we couldn't make a list of United clangers without turning to the mistakes that have saddled him since 2018 at least a few times.

Few of them were more head-scratching than when De Gea fumbled a routine strike from Ismaïla Sarr into his own net a la Peter Schmeichel vs Sheffield Wednesday in 1998.

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6. De Gea distribution disaster vs Everton

However, just a few weeks later, the Spanish shot-stopper provided us with another bewildering moment as he took way too long on the ball in his own penalty area at Goodison Park.

The result? Dominic Calvert-Lewin was alive to the situation and De Gea watched in horror as his eventual clearance was deflected into the net by the future England international.

7. Whole defence lobbed by Simon Mignolet

United fans made a habit out of roasting Mignolet when he played between the sticks for Liverpool, but the Belgian goalkeeper completely mugged them off in the Europa League in February.

That's because Mignolet crazily crated a goal for Emmanuel Bonaventure by simply booting the ball over the United defence and watching with joy as Sergio Romero was easily lobbed. 

8. Man Utd carved open vs Tottenham

We're just going to refer you to Roy Keane here: “I am staggered at Maguire, staggered that an international player can just get done by this. Maguire and De Gea – I wouldn’t even let them on the bus after the match.

"Get a taxi back to Manchester. Shocking! Maguire, I am disgusted with him and De Gea. You should hang your heads in shame.”

9. Maguire marking his own player vs Southampton

Now, Maguire has admittedly become something of a pin cushion at United over the last few months and we're inclined to think some rival fans direct the blame towards him a little too easily.

That being said, we still don't have an explanation for why Maguire appeared to be marking Aaron Wan-Bissaka mere seconds before Michael Obafemi scored a last-minute equaliser at Old Trafford.

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10. No-look defending and poor marking vs Sevilla

Ok, ok, we're only briefly going to mention Maguire coining the phrase 'no-look defending' because we can't deny the fact that screenshots of him seemingly ignoring a Sevilla attack were amusing.

However, far more egregious was the performance of Williams in the place of Shaw, while Lindelof won himself an earful from Bruno Fernandes for some questionable defending of his own.

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11. Maguire carnage vs Tottenham

We promise this is the last error involving Maguire but, once again, there is only so much you can excuse what might be the worst mistake on the list - and it proved damning in a 6-1 annihilation.

Maguire failed to head the ball clear twice, including pinging it towards Eric Bailly, before seemingly pulling down Shaw in a baffling decision that only made it easier for Tanguy Ndombele to score.

12. Paul Pogba conceding penalties

In order to save Pogba three spots on this list, we've rolled his recent fascination with conceding penalties into one with both the Spurs and Arsenal incidents proving incredibly reckless.

However, the most unforgivable of the errors came against West Ham when he literally blocked the ball with both hands. It was coming his way at speed, sure, but better to try dodging it than give away an instant penalty.

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13. Everything vs Istanbul Basaksehir

And here we are. We're not given going to try and explain what happened for United in Turkey, so we're just going to mold their entire performance together into one big disasterclass. 

Unlikely thirteenth, that's for sure.

GIVEMESPORT's Kobe Tong says

Now, look, I think Solskjaer is due his fair share of criticism in this United debacle, but let the 13 calamities above remind us all that some things are simply out of his hands. 

De Gea is one of the best goalkeepers in the sport and Maguire, whether you like to admit it or not, can be world-class on his day, so it must be infuriating to have watched them continuously drop so many clangers.

Yes, defensive mistakes can be ironed out and mitigated by coaches, but they can never be totally eradicated and United need to pull themselves together before their manager bites the bullet.

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You only need to look at their other results in the Champions League to see that there is so much quality in this United side and they can still make a good season out of 2020/21.

But as long as defensive errors continue to rear their head every ten seconds, United growth in the post-Sir Alex Ferguson era will forever be stunted.