Troy Parrott scored twice for the host nation, while it was contrasting emotions for Portugal's number seven as Ronaldo received the first red card of his storied international career, in his 226th match.

AZ Alkmaar striker Parrott gave Ireland the lead after 17 minutes when a deep corner towards the far post was headed across goal by Liam Scales, and Parrott was on hand in the six-yard box to convert past Diogo Costa.

Chiedozie Ogbene struck the upright with a low, curling effort, but Parrott doubled the lead on the stroke of half-time as he managed to squeeze the ball in at the near post after taking down a hopeful long pass from Dara O'Shea.

Portugal's hopes of a turnaround were all but gone when Ronaldo was sent off after a pitchside video assistant referee (VAR) review showed the forward caught O'Shea with his elbow in a moment of frustration.

Goncalo Ramos forced a late save from Caoimhin Kelleher, but Heimir Hallgrimsson's side is three points behind Portugal in Group F and trails second-placed Hungary by only one ahead of their meeting on Monday (AEDT), which will bring the curtain down on its campaign.

Portugal boss Roberto Martinez insisted his side must quickly move on from this defeat.

“It's a game to forget. It happens in football,” he said.

“Everything that could go wrong, went wrong. And it went well for Ireland. We talk a lot about the set-piece, the transition, the corner goal.

“We lacked purpose. We showed fight until the end with 10 men, we played the last minutes with a lot of heart, but Ireland deserved to win.

“The strength of the stadium that Ireland had is what we need, and we know we can count on it in the last qualifying game to confirm our presence at the [FIFA] World Cup.”

Martinez said he believed there was no malicious intent behind Ronaldo's action that saw him dismissed.

"Of course, we spoke. I think it's difficult for a player like Cristiano, who's in the box,” Martinez added.

“And today he had two defenders constantly in physical contact. There's no violence. He tries to push the defender away and he was unlucky that the VAR.

“The angle of the images [makes it look] worse than what happened. It's Ronaldo's first red card for the national team. It's incredible."