The Champions League returned to take centre stage as the league reached it's halfway point for those in action.

And it was a night of shocks and underdogs as Real Madrid, Manchester City and Bayer Leverkusen all astonishingly ended on the losing side.

Here's what we learnt from Tuesday's drama.

Champions showing a worrying trend

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Reigning champions Real Madrid have not had a good few days.

Thrashed 4-0 in El Clasico, Vinicius Jr was then snubbed for the Ballon d'Or. Now, they face a real risk of not making the Champions League knockout stages after falling to a tame 3-1 loss at home to Milan.

It leaves Los Blancos on just six points from four games, with trips to Liverpool, Brest and Atalanta as well as a home tie with Salzburg.

More worryingly, they cannot stop falling behind, having done so in three of their four Champions League games so far.

Plenty for Ancelotti to ponder at the Bernabeu.

Ruben Amorim gets early advantage over Guardiola

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All eyes were firmly on Sporting CP's clash with Manchester City after it emerged earlier in the week that Sporting boss Ruben Amorim would be taking the vacancy at Old Trafford.

And he will already be a popular man on the Red half of Manchester after his side came from a goal down to thrash Pep Guardiola's side 4-1 with goals either side of half time.

More importantly, he ended Manchester City's UCL unbeaten record, which stood at 26 games after they broke Manchester United's 16 year old record in their last game.

Is this some early evidence of what's to come in the Premier League?

Celtic making shock charge for the knockouts

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After being thrashed 7-1 by Borussia Dortmund on Matchday 2, there was little hope that Celtic would be in the mix to reach the knockout stages of the competition.

However, two games later they sit on seven points, ahead of the likes of Real Madrid and Milan, courtesy of a memorable 3-1 home win over German giants RB Leipzig.

In their final four games, Rodgers' side face Club Brugge, Dinamo Zagreb, Young Boys and Aston Villa.

Could they make the knockout rounds for the first time since 2012/13?

The Arne Slot train rolls on

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Few would have predicted how well Arne Slot has taken to life at Liverpool.

But after taking over from iconic manager Jurgen Klopp, he has fitted in seamlessly, with his only blemish coming against Nottingham Forest.

Faced with a Bayer Leverkusen side who had lost just twice in all competitions since Jordan Henderson last played for the Reds, they romped to a 4-0 win over ex-player Xabi Alonso as Luis Diaz grabbed a hat-trick to take them top of the pile at the midway point.

People keep expecting them to lose, but they keep defying the odds, and now sit top of both the Premier League and Champions League.

Could it be their year once more?

It's getting tight at the top

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Though only Liverpool have picked up maximum points from four games so far (Aston Villa can join them tomorrow), it is still very tight at the top of the table.

Sporting CP and Monaco's wins helped them into second and third place respectively, while Manchester City lead a gaggle of nine clubs stuck on seven points, of which two can move to ten points tomorrow evening.

Five more teams sit just a point further back in what is shaping up to be an intriguing second half of the Champions League league stage.

Though unpopular to begin with, the league format could well prove a winner.

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