Romelu Lukaku scored his first ever Chelsea goal - almost a decade after his debut - as Thomas Tuchel's team deservedly beat Arsenal.
Lukaku, who was at Chelsea as a teenager, started at the Emirates after his £97.5m signing from Inter Milan and looks to have given the Blues an ominous new dimension.
His hold-up and link-up play caused Arsenal problems all day - and the Belgian duly gave them the lead.
Lukaku was involved in the build-up and then finished the move from close range into an empty net from Reece James' pass.
James got the second himself as he slammed the ball into the roof of the net from Mason Mount's pass to make it two wins from two in the league.
Lukaku almost made it 3-0 but his header was tipped onto the bar by Bernd Leno.
Arsenal, missing centre-back Ben White through Covid, have now lost more London derbies in the Premier League this season than last - after just two games.
It is only the third time Arsenal have lost their opening two Premier League matches in a season.
Afterwards, Blues manager Thomas Tuchel said: "It was a good match of football, fantastic atmosphere from the start. It is not like we controlled the game for the entire 90 minutes. I thought at times in the first half we were sloppy. I felt a bit like we had heavy legs. So in some moments, we felt like we suffered a little bit physically and had easy ball losses.
"But in general I am really happy and it was a deserved win. and it is the best way to start a season, to not concede goals and give chances away.
"What a start for Lukaku. In the beginning he struggled to touch the ball at a little bit. Then he was very well integrated. He proved his value for the squad already, he linked really well with Mason and Kai up front and gave something to the game that we did not have already.
"We can play very direct and to the last line. He can hold the balls but he is also very strong in turning and winning the one-on-ones he is a constant dangerous player witha big personality that helps.
"Reece James was good, he came back with a lot of confidence from the Euros, I think he can still improve in sharpness and decision making and I think he can be more confident in going forward but I hope it helps him to assist and to score today, and at the same time he was a key player to keep Tierney on our right side so well done.
"We are still in reality, we was fourth last season and we needed help from our rivals. We are capable to produce top performance this is what we have proved in the last half a year and we would like to continue. We have the feeling that we have something to improve and we just want to close the gap.
"If you want to compete for any title we need a strong squad and it is my job to manage the squad and we need a good balance between competition and friendship and pushing each other. Because this was maybe the key factor in the last half a year. We have a strong squad and we have a lot of games to play."
