Ronaldo, who also converted two penalties in the 3-0 win at Barcelona on Tuesday, fired into the middle of the goal in the 78th minute and struck again 11 minutes later, taking his league tally this season to 10.
"I'm very proud of reaching this number with the Vecchia Signora jersey, but guess what: I also have my mind already set on the 100 goals for Juve," Ronaldo wrote on social media.
Juve, chasing a 10th successive Serie A title, are fourth with 23 points from 11 games and are still unbeaten, although they have drawn five times. Genoa, who narrowly escaped the drop last season, are one off the bottom with six points.
Juve had 71% of possession but, not for the first time, Andrea Pirlo's team struggled to open up stubborn opponents from the wrong end of the table.
"We had to put the Barcelona game out of our minds," said Juventus coach Andrea Pirlo. "We knew we were up against a team that wanted to close ranks, so we had to be patient.
"The most important thing was our attitude -- we couldn't wait for them to play but we had to attack them."
It took them 57 minutes to break through when Weston McKennie flicked the ball to Paulo Dybala and the Argentine beat Mattia Perin with a shot inside the near post for his first league goal of the season.
Dybala had a goal disallowed for offside and Ronaldo sent a free header straight at Perin before Juventus eventually wore Genoa down.
Perin then upended Alvaro Morata after Genoa gave the ball away in defence and Ronaldo duly blasted the ball into the roof of the net.
"It was annoying to concede a goal at literally the first shot on target, especially a few minutes after we broke the deadlock, but we recovered from it," said Pirlo.
"Dybala needed the goal to unblock himself mentally and physically. We've been waiting for this and now we expect even more from him."