The managers kept their cool, both sets of fans heeded appeals for calm – but on the pitch it was mayhem.
Forty days after they both last played a game, Manchester City and Liverpool wasted no time in producing a typically high-octane encounter, one in which no quarter was given.
When the dust had settled on the frenetic meeting between the two great rivals, it was City who emerged victorious, to book their quarter-final place.
Holders Liverpool went out, leaving the Champions League and FA Cup as their only chances of silverware this season, given their title challenge is over before Christmas.
After both clubs urged fans to behave and end the toxic rivalry that has emerged in recent encounters, City boss Pep Guardiola and opposite number Jurgen Klopp were on best behaviour.
Tempers flared on the pitch near the end, when Rodri and Fabinho clashed, sparking a melee in the middle of the pitch as players from both sides sought retribution.
But this match was all about the chaotic, end-to-end contest between the two best sides in England in recent years, the thrilling entertainment a fitting way to mark the return of the domestic game.
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City's last encounter before the World Cup break ended in a shock 2-1 home defeat to Brentford, allowing Arsenal to extend to five points their lead at the top of the table.
Liverpool, in contrast, had signed off for the break with a 3-1 win at home to Southampton, although that still left them in sixth place, seven points off fourth spot.
Both managers picked strong sides, mindful of the need to get minutes in the legs of players not involved at the World Cup and to establish some rhythm after such a long lay-off.
Ahead of the game, Guardiola said City's players who had been in Qatar were sharper than those who had enjoyed a six-week break, with six of his World Cup stars included in his line-up.
Klopp, in contrast, included a solitary World Cup star in his starting line-up, Uruguay striker Darwin Nunez, with Jordan Henderson and Fabinho, who also played in Qatar, on the bench.
Erling Haaland took just 10 minutes to continue where he left off before the World Cup break, getting ahead of Joe Gomez to score his 24th of the season.
Liverpool were level 10 minutes later, James Milner picking out the unmarked Fabio Carvalho, who was able to roll the ball into the far corner beyond City keeper Stefan Ortega.
City twice came close to restoring their lead just after the half-hour mark, Ilkay Gundogan with a goalbound shot blocked, then a header from Nathan Ake was turned away by Caoimhin Kelleher.
Fans were still taking their seats for the second-half when Riyad Mahrez put City back in front, 66 seconds after the restart, only for Mo Salah to level within a minute at the other end.
City restored their lead a minute before the hour, a short corner between Cole Palmer and Kevin De Bruyne ending with the latter slinging in a cross which was headed in by Ake.
Nunez wasted a glorious chance to make it 3-3 in the 71st minute, racing clear, only to screw his angled shot wide of the target, with City holding out to advance at Liverpool's expense.
