Juventus leapfrogged Inter at the top with a thrilling 2-1 win in the Derby d'Italia at San Siro on Sunday.
Goals from Paulo Dybala and Gonzalo Higuain saw Juve move a point clear of Inter, who saw their perfect start to the league season snapped by the Bianconeri.
Ronaldo, who rattled the crossbar and had a goal ruled out for offside, used Instagram to celebrate Juve's fourth consecutive league victory.
The five-time Ballon d'Or winner wrote: "Very strong performance by the team today! Great feeling to be on the top of the table again! #finoallafine #forzajuve #liveahead."
A fine fourth-minute goal from Dybala put Juve ahead before Lautaro Martinez equalised via the penalty spot 14 minutes later.
However, Higuain had the final say after coming off the bench and scoring the winner with 10 minutes remaining in Milan.
Juve now sit top the table heading into the international break, with Maurizio Sarri's men returning to action against Bologna on October 19.
After an unconvincing start in Turin, Sarri believes his side are starting to show all the right signs as they look to claim yet another Serie A title
"Overtaking at the top means little right now. The most significant element is that we played well, with character and determination against a side that had won every game so far,” Sarri told Sky Sport Italia .
"We started well and had the right approach in a fiery atmosphere, so that’s a good sign.
"I feel we can still improve a great deal more. It’s a gradual process, the team has strong individuals and so much strength in depth. It means at the moment we can get results, even if we are not playing at 100 per cent.
"I think this team has already made important steps forward in its passing. What we need to work on is dominating the match, having territorial supremacy, pressing better and more, taking away any attacking initiative from the opposition so that we can spend our whole time in the opposition half."