Raheem Sterling scored an 11-minute hat-trick as Manchester City came from behind to thrash Atalanta 5-1 - but the result was marred by an injury to makeshift centre-back Rodri.
City maintained their 100 per cent record in Champions League Group C - and Atalanta remain without a point after three games - but there was concern for Pep Guardiola after Rodri was forced off with a hamstring injury in the first half.
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City are now five points clear at the top of Group C after Shakhtar Donetsk were held to a 2-2 draw by Dinamo Zagreb, but they ended the night on another low note as Phil Foden was sent off for two bookable offences.
Man City: Ederson (7), Walker (6), Rodri (6), Fernandinho (6), Mendy (6), Foden (6), Gundogan (7), De Bruyne (7), Mahrez (7), Sterling (9), Aguero (8).
Subs: Stones (5), Otamendi (6), Cancelo (5).
Atalanta: Gollini (6), Toloi (5), Djimsiti (5), Masiello (4), Castagne (5), de Roon (6), Freuler (5), Gosens (6), Malinovsky (6), Gomez (4), Ilicic (6).
Subs: Muriel (5), Hateboer (5), Pasalic (5).
Man of the match: Raheem Sterling.
By then, Sergio Aguero (34, 38 pen) had cancelled out Ruslan Malinovskiy's opener from the penalty spot (24), before Sterling took centre stage.
The England forward had already provided Aguero with both his goals before three predatory finishes (58, 64 and 69) saw the Premier League champions pull clear.
How City bounced back in style
Guardiola set his players the task of proving him wrong by showing they are mentally prepared to win the Champions League, but it was Atalanta who made the brighter start.
Robin Gosens ran into the space vacated by Kyle Walker down the left to cross but Timothy Castagne somehow headed over under pressure from Benjamin Mendy from point-blank range.
Aguero, making his 100th appearance in European football, very nearly broke the deadlock when his curled right-foot shot was brilliantly tipped around the post by Pierluigi Gollini - but four minutes later, it was the visitors who struck first.
Malinovskiy began the move as he broke free in midfield before feeding Josip Ilicic down the right and when the Slovenian striker cut inside Fernandinho, he was brought down just inside the box.
The Israeli referee Orel Grinfeld was well-placed to spot the infringement, and Malinovskiy strode forward to confidently send his penalty to Ederson's right as he flung himself in the opposite direction.
Phil Foden was handed a starting place as Fernandinho and Rodri were again paired in central defence for Manchester City.
Kyle Walker overcame illness to return at right-back while Sergio Aguero was named up front after being rested last weekend.
Riyad Mahrez also came back into the side but both Bernardo Silva and David Silva were among the substitutes.
But having conceded their first goal in the competition this season, City responded in style when the lively Sterling crossed for Aguero to poke home an immediate equaliser through the legs of Gollini.
And it was Sterling who once more provided the hosts the chance to complete the turnaround only four minutes later as the England forward's trickery forced Andrea Masiello to bring him down inside the box.
Aguero made no mistake as he dispatched his penalty firmly to Gollini's right - but City's celebrations were cut short moments later after Rodri broke down with a hamstring injury, with John Stones replacing the Spaniard.
When asked about the extent of the versatile midfielder's injury, Guardiola said afterwards: "We don't know about Rodri yet. Hopefully it will be around 10 days if it's not broken. If it is broken, he'll be out three weeks to a month. It looks like a hamstring injury."
Kevin De Bruyne tested Gollini with a strike from range 10 minutes into the restart, and the Belgian playmaker was instrumental in setting up City's third as it was his weaving run down the right that allowed Foden to nudge the ball into the path of Sterling for a simple finish.
With 58 minutes on the clock, Sterling was only just getting started as he started and finished a brilliant sweeping move, collecting Ilkay Gundogan's pass six minutes later to charge past two defenders and send Gollini the wrong way.
It was now a race to the match ball between Aguero and Sterling, and it was the latter who wouldn't be denied as he showcased his predatory instinct to meet Riyad Mahrez's cross to complete his second treble of the season.
But City's evening ended on a sour note with Foden's dismissal. Six minutes after being cautioned for tugging back Malinovskiy, the 19-year-old did likewise to Marten de Roon to receive a second booking to spoil an encouraging second start of the season.
What the managers said
Manchester City manager Pep Guardiola: "We knew that if they won duels they could create chances, and they did that in the first half and even in the second half.
"Raheem and Sergio were good but they were a really tough opponent that we knew they would be after finishing third in one of the toughest leagues in the world last season.
"The result was good but it required an incredible effort. They played well with the wing-backs and they are a top team. We have nine points and we need one more win to be in the next stage."
Man of the match - Raheem Sterling
Sterling was electric throughout. Even when City were behind, he was the one creating chances, taking players on and making things happen, a non-stop turbocharged livewire.
He scored a clinical hat-trick in just 11 minutes, taking his tally to 12 goals in 13 City games this season, and making him the eighth Englishman to score a Champions League treble.
He could and probably should have had a fourth when put through one-on-one by Foden, but criticising him for that would be churlish.
"All the credit is for him," Pep Guardiola said. "He's a guy whose physicality is incredible. He is so strong. A day after a game, he could play another. His regeneration is incredible and he can play both sides. He is an extraordinary player."
Asked if the 24-year-old could get even better, Guardiola said: "It depends on him, his desire, and I think he has that - the desire to be better."
Analysis: City provide Pep with perfect response
Sky Sports' Ben Ransom:
If Pep Guardiola was looking for a response by saying his team weren't ready to win the Champions League, then this was it.
Raheem Sterling's first European hat-trick along with two goals from the ever-reliable Sergio Aguero was about as clinical as Pep could have wanted to see.
It'll be an anxious wait to see whether Rodri's apparent muscle injury keeps him out for any length of time, but the fact that first John Stones and then Nicolas Otamendi came through their substitute appearances unscathed will be a boost.
Pep was able to rotate players with half-an-eye on the next Premier League game here against Aston Villa - taking off the likes of Kevin De Bruyne and Benjamin Mendy.
Maximum points from the group so far has Manchester City well-set for qualification which is essential given that the trip to Anfield immediately follows the next Champions League game away at Atalanta in three weeks' time.
- Manchester City's victory was the biggest for an English side against an Italian side in all European competitions since Manchester United's 4-0 win over Milan in 2010.
- Atalanta have become the first Italian side to lose their first three Champions League games, and the first side overall since Otelul Galati in 2011-12.
- Manchester City have won three of their last five Champions League games in which they conceded the first goal (D1 L1).
- Man City's Sergio Aguero became just the second player to score 20 Champions League goals at an English stadium (21), after Ruud van Nistelrooy at Old Trafford (23).
Manchester City host Aston Villa in the Premier League on Saturday (kick-off is at 12.30pm). Atalanta are back in Serie A action on Sunday with Udinese visiting the Atleti Azzurri d'Italia.
City's next Champions League fixture is the return meeting with Atalanta on November 6.