Ronaldo left the field in tears after being sent off during Wednesday night's Champions League win at Valencia, and it looked as though he would endure another frustrating evening when he squandered a host of chances at the Stadio Benito Stirpe.
However, the five-time Ballon d'Or winner eventually made the breakthrough late on to put Juve on course for a fifth straight win at the start of the new season.
"He had many chances and that happens because good balls always end to players that are able to score goals in the box. He missed some of these chances, on a few occasions he has been unlucky with the rebounds, but his strength is the fact that he is always into the match, even if he doesn't score straight away," Allegri told the club's official website.
"And that's what happened because to score a goal like that towards the end means that he has a mentality stronger than the others. We were expecting a game like that.
"We came into this match having played with 10 men for 70 minutes in midweek and it was one of those games that become really tricky if you don't find an early breakthrough. I'm happy with the way the lads kept working the ball towards Frosinone's area quickly and calmly. Eventually the goal came for us."
Juventus face Bologna on Wednesday night looking to maintain their status as the only perfect team remaining in Serie A.