Ronaldo opened the scoring in Gelsenkirchen with a header before setting up Marcelo's second-half goal at Veltins Arena on Wednesday.
The Portugal star had gone three games without a goal, including being sent off at Cordoba on January 24.
But Ronaldo ended that goalless run, and Ancelotti said he never doubted the 30-year-old would return to his best.
"Cristiano played well. He scored and provided an assist. He's back," Ancelotti was quoted as saying by the club's website.
"The team does not panic when Cristiano fails to score in one or two games. Everyone knows that if he doesn't score in one or two games, he will in the next match."
Ronaldo got on the end of a Daniel Carvajal cross to open the scoring with a header in the 26th minute.
The forward set up the sealer, touching a pass into Marcelo – who fired a rasping drive into the top corner from just outside the area.
Ancelotti lauded his team's performance and said they were in complete control after Ronaldo's goal.
"We needed to play like that, with that kind of attitude and performance. And everything worked out well in the end," the Italian said.
"The team were serious and efficient and the opposition were pegged back from the get go. Once we got the first goal, we controlled the game."
