The forward began his new chapter in typically brilliant fashion by doing what he does best: scoring goals. Newcastle were the victims on this occasion.
Manager Ole Gunnar Solskjaer decided to start his new signing and the roof was nearly lifted off Old Trafford when one of football's greatest ever players emerged from the tunnel.
And he quickly got to work.
The Portugal captain tapped in the easy rebound for the first goal of his second spell at the club to make it 119 goals in total.
A crowd full of 'Ronaldo 7' shirts erupted, while in the private family boxes, the scenes were much more emotional.
Ronaldo's mother, Dolores Aveiro, was spotted crying by a fan, who managed to snap a picture of the moment she was overcome with emotion.
She has been with her son throughout his career and rise to the top of the sport, often pictured with him during trophy celebrations.
And although she's likely seen the majority of his 787 goals, which is believed to be the most of any player in the history of professional football, the opener hit home.
It was at Old Trafford where he made his name, moving to Manchester from Portugal in 2003 when he was just 18.
Fans have given him a welcome return and the player has said he feels like he is back where he belongs.
The 36-year-old later scored goal no.120 in the 4-1 win to increase the expectation on the club to win the Premier League title.