Inter Milan laid down an early title marker on Saturday by handing out a 5-1 derby hammering to AC Milan and going it alone at the Serie A summit, while champions Napoli were held 2-2 at promoted Genoa.
Four wins from their opening four matches have Inter leading the pack with a perfect 12 points, two ahead of their other fierce rivals Juventus who beat Lazio 3-1 in the day's early match.
Milan sit a further point back in third after a humiliating first defeat of the season before they welcome Newcastle United in the Champions League on Tuesday.
Spurred on by the majority of a heaving and raucous San Siro crowd, Inter claimed their fifth straight derby win in all competitions thanks to a Henrikh Mkhitaryan brace, Marcus Thuram's rocket and two late strikes from Hakan Calhanoglu and Davide Frattesi.
Simone Inzaghi's side claimed the points with a display which showed why they got past Milan to reach last season's Champions League final and confirmed their status as early favourites to beat their local rivals to a 20th Scudetto.
"We've started the season brilliantly and we want to keep going," Mkhitaryan told DAZN.
"We're all here for the same goal, and I don't care who plays... the coach will pick whoever gives their all for the second star (on the shirt for 20 titles)."
Thuram continued his fast start in an Inter shirt, the new man also crucial to Mkhitaryan's fifth-minute opener.
- Inter smash Milan -
France forward Thuram bundled past Malick Thiaw before finding Federico Dimarco whose mishit shot was guided home by the former Armenia midfielder.
And Thuram then underlined Inter's superiority seven minutes before the break after a lightning breakaway started by Lautaro Martinez, collecting from Denzel Dumfries before cutting inside the hapless Thiaw and crashing in an unstoppable shot from the edge of the area.
The match looked dead and buried with 45 minutes to play but Rafael Leao halved the deficit in the 57th minute when he rolled in his second of the season after being brilliantly put through by Olivier Giroud.
Leao's finish was the first goal conceded by Inter this term and as a violent downpour descended on the San Siro, Mkhitaryan silenced Milan's loud "away" support with his deflected second of the evening after being fed by Martinez.
Calhanoglu's 79th-minute penalty and a neat stoppage-time finish from Frattesi, fresh from Tuesday's double for Italy at the same ground, rubbed salt into wounds for Milan and coach Stefano Pioli.
"I don't think we need to apologise to our fans. Do you think we wanted to concede five goals to Inter?" said a defiant Pioli who in 2023 has lost every Milan derby to an aggregate score of 12-1.
"We're disappointed, but you ask for forgiveness when you deliberately don't do something."
- Napoli salvage point -
Napoli's title defence continued to stutter at Genoa where the champions came back from two goals down to snatch a point late on.
Rudi Garcia's side, beaten by Lazio before the international break, trail Inter by five points following the draw at the Stadio Luigi Ferraris which came thanks to strikes in the final 15 minutes from Italy internationals Giacomo Raspadori and Matteo Politano.
"We've got work to do, but we had very little time to prepare for this match because a lot of players only came back (from international duty) yesterday," said Politano to Sky Sport in Italy.
Mattia Bani headed Genoa into the lead five minutes before the break before Italy striker Mateo Retegui swept in the hosts' second from Kevin Strootman's pass in the 56th minute.
Retegui has scored twice since signing from Boca Juniors in July and Saturday's strike looked likely to give Genoa a stunning second win of the campaign.
But Napoli didn't give up and were back in it when Raspadori arrowed in his first goal of the season in the 76th minute.
And Politano salvaged a draw for Napoli with six minutes remaining with a brilliant volley from Piotr Zielinski's lofted pass.