United was generally tame once again in the 1-1 draw, but Ronaldo did at least ensure the Red Devils avoided suffering three successive Premier League defeats for the first time since 2015.
Just 119 seconds after Marcos Alonso had put Chelsea in front at Old Trafford, Ronaldo latched on to Nemanja Matic's scooped pass over the defence and drilled home.
Ronaldo has now scored eight of United's nine most recent goals in the Premier League, with Fred the only other player to net for the club this month.
Friday's (AEST) goal took Ronaldo to 17 for the season in the league, a haul bettered by only Mohamed Salah, but Rangnick was keen to highlight the striker's all-round performance as he saluted his defensive work rate.
Ronaldo's future beyond the end of the season does look uncertain with United set for a massive clear-out and rebuild, but Rangnick can see a role for the 37-year-old if he is able to replicate such performances.
Speaking to Sky Sports, Rangnick said: "Not only the goal he scored today, also his whole performance, attitude and how often he helped out in our own half.
"At 37, a player like him – this is not normal to do that. He showed that today. If he plays like he played today, he can still be a great help for this team.
"In the end it's both Erik's and Cris' decision what they want to do, it's not for me to speak about that.
"But as I said, today the performance of Cris was really great."