Jack Grealish helped Manchester City negotiate a tricky Champions League opener and sensationally defeat RB Leipzig 6-3 at the Etihad Stadium.

Club-record signing Grealish made his European debut a memorable one on Wednesday, adding to an early assist for Nathan Ake with a sublime second-half strike.

City – in action in this competition for the first time since last season's final defeat to Chelsea – wobbled a little between those two efforts, benefitting from Nordi Mukiele's own goal and a Riyad Mahrez penalty but conceding twice to Christopher Nkunku.

Even after Grealish's goal, Nkunku's hat-trick strike caused further concern, only for Joao Cancelo and substitute Gabriel Jesus to notch numbers five and six for City and clinch three vital points in a tough Group A that also features Paris Saint-Germain.

Both sides will have to defend better against PSG, with Leipzig's woes evidenced as Ake towered over two opponents to head in Grealish's corner before Mukiele inexplicably nodded Kevin De Bruyne's awkward delivery past his own goalkeeper.

Mukiele soon put his head to better use, directing the ball back across goal for Nkunku to nod beyond Ederson, but back came City before the break, this time aided by Lukas Klostermann, whose elbow blocked Ferran Torres' header and allowed Mahrez to dispatch a thumping spot-kick.

The second half followed a similar pattern, with Leipzig twice working hard to get back into the game and then quickly falling further behind.

Grealish's pinpoint finish after cutting in from the left cancelled out another header from Nkunku, who completed his treble shooting across Ederson from the right side of the area.

Cancelo drove in from 25 yards, however, and then provoked a red card from former City man Angelino – dismally late to a challenge when already booked – with time remaining for a scruffy close-range sixth from Jesus.

What does it mean? Stylish City reach Champions League milestone

Without John Stones and Aymeric Laporte, City certainly could have defended better, but this was a mightily impressive way to bring up 50 wins in the Champions League.

Only Real Madrid (88) have made it to that mark in fewer games than City's 91, although Pep Guardiola's goal will be to finally make some progress towards the LaLiga giants' most notable record – their 13 European crowns to City's none.

Wow Cancelo

While Grealish weaved his magic on the left, Cancelo did likewise on the right, marauding forward from full-back. A wonderful goal was his only shot, while the Portugal international also created just a single chance, but that did not tell the whole story.

The opportunity he forged led to the penalty from one of three crosses, and he would have had an assist if not for a tight offside call against Torres.

Clearly winning his personal battle on that flank against Angelino, Cancelo won all of his five duels, earning two fouls – including for the dismissal – and gaining possession on 10 occasions.

Naughty Nordi

Angelino may have seen red, but Mukiele – the other full-back – will be in the bad books after this one. This was a dismal display up against Grealish.

Even besides his comical own goal, which an assist then cancelled out, Mukiele came out on top in just 38.5 per cent of his duels and gave away two fouls.

Key Opta Facts

- This was Manchester City's highest scoring Champions League game, surpassing the eight goals netted in their 5-3 victory over Monaco in February 2017. 

- This was Pep Guardiola's 300th match in charge of City in all competitions (W219 D36 L45), and the 750th game of his managerial career (W547 D113 L90). 

- Grealish became the first Englishman to both score and assist on their Champions League debut since Wayne Rooney versus Fenerbahçe in September 2004.

- Christopher Nkunku, who became the first RB Leipzig player to score a Champions League hat-trick, became only the second player to score a hat-trick against Man City in the competition after Lionel Messi in October 2016. 

What's next?

City have serious competition at home as well as abroad this season and cannot afford to slip up against Southampton on Saturday, when Leipzig will be hoping to bounce back at Cologne.