Ronaldo scored twice late in the game to help his country from behind against the Irish.
John Egan’s first-half header put Ireland ahead. Ronaldo also had a penalty saved by 19-year-old goalkeeper Gavin Bazunu in the opening 45 minutes.
But the legendary striker finally broke Ali Daei’s record of 109 international goals in the 89th minute. He had been tied with the former Iran forward since scoring five goals at Euro 2020.
Ronaldo then scored again six minutes into stoppage-time to inflict a crushing defeat on Stephen Kenny’s side.
His first goal earned him a place in the Guinness World Records book and he celebrated the achievement with a warning to rivals that he will continue to break records for Man Utd and Portugal.
The post was accompanied by a bicep emoji.
Ronaldo completed a sensational return to United on transfer deadline day, ending a remarkable saga.
He returns to Old Trafford 12 years after he departed in a then-world record GBP90m transfer to Real Madrid.
Having been booked for removing his shirt during the celebrations for his second Portugal goal on Wednesday, Ronaldo is suspended for his country’s next World Cup qualifier against Azerbaijan.
He has decided to travel back to Manchester early and will hold discussions with boss Ole Gunnar Solskjaer.
“Well, we had a chat, but of course I’m going to have time to speak with him face to face, to know what he expects,” Ronaldo told United’s official website.
“As you know, I played with him for two or three years at Manchester United, so I have a good relationship with him but now with a different role. I’m a player and he’s a coach.
“But it doesn’t matter, my relationship with him is great and I’m there in Manchester to help the team achieve his results and the coach can count on me for whatever he wants.
“So I’m available for everything.”