Serie A leaders Inter Milan defeated city rivals AC Milan 2-0 at the San Siro stadium on Saturday to maintain their 100% start to the campaign.
Second-half goals from Marcelo Brozovic and Romelu Lukaku secured the win for Inter who deserved their victory and could have made the result even worse for Marco Giampaolo's side in the final stages.
After the disappointment of a 1-1 draw at home to Slavia Prague in the Champions League on Tuesday, Inter delivered a performance that will raise hopes of a serious bid for a first 'scudetto' in 10 years.
For coach Antonio Conte, in his first season at the club, the derby victory was a sign that his approach is beginning to work.
"It's a derby and those are always special games, never easy to predict, especially when both teams are so prestigious as Inter and Milan," Conte said.
"The lads played a good game in every aspect. We were coming off a performance in the Champions League that left a bitter taste in the mouth and perhaps that fired us up even more to go into the derby in the right way.
"It's a deserved victory, I am happy for our fans, because the derby is always the derby."
Inter, who are now unbeaten in the last seven league clashes with Milan, grabbed the lead thanks to a deflected strike from Brozovic in the 49th minute.
A quick free kick from Stefano Sensi found Brozovic on the edge of the box and his low drive took a huge deflection off Rafael Leao and beat the wrong-footed Milan keeper Gianluigi Donnarumma.
The assistant flagged Lautaro Martinez offside but a VAR review ruled that he was not interfering with play.
It was the third time that VAR had been used in the game — a 23rd-minute effort from Milan's Hakan Calhanoglu was ruled out for handball by Franck Kessie and then Inter's Lautaro Martinez had his tap-in disallowed for offside after Danilo D'Ambrosio's bicycle kicked had been parried out.
Lukaku made sure of the win with a 78th-minute glancing header from a Nicolo Barella cross from the left for his third goal since his move from Manchester United.
Inter, who went close to a third when Matteo Poltano clipped the bar and then Andrea Candreva hit the post, have 12 points from four games, two more than defending champions Juventus, who earlier beat Verona 2-1.
Giampaolo said Milan, who have two wins from their opening four games, had shown their inexperience.
"We were too hesitant at the start, then as the game progressed Inter showed their greater experience," he said.
"The goal broke the deadlock and I was not happy to see that we reacted in an emotional way, becoming less organised and less united."