Before Portugal's World Cup qualifying defeat by the Republic of Ireland, Cristiano Ronaldo said he would "try to be a good boy" to keep Irish fans off his back.

In the heat of battle, however, Ronaldo ensured he joined Thierry Henry as one of Irish football's great pantomime villains.

With Portugal trailing 2-0 to Troy Parrott's first-half double, Ronaldo clashed with Dara O'Shea in the Irish penalty area on the hour mark.

Jostling for position as he awaited a cross, the 40-year-old shunted his elbow into O'Shea's back, sending the Ipswich defender tumbling to the turf and sparking a strong reaction from the Irish players and fans at Aviva Stadium.

Referee Glenn Nyberg spotted the incident and showed Ronaldo a yellow card, but having been urged to review the incident on the pitch-side monitor by the video assistant referee, the Swedish official came back with a red.

Ronaldo, who had endured a frustrating night up to that point, thought better of quietly accepting his punishment and proceeded to sarcastically applaud the Irish fans and exchange words with Republic of Ireland boss Heimir Hallgrimsson before exiting the stage.

He could now potentially miss the start of Portugal's World Cup campaign if they qualify.

It was an eventful end to an unexpected yet intriguing spat between Ronaldo and Hallgrimsson.

Ronaldo previously had good memories of Dublin. Sixteen years ago, he played his first game for Real Madrid - a pre-season friendly against Shamrock Rovers - in the Irish capital.

In his eve-of-match news conference, Ronaldo said it was "lovely" to be back.

However, he also accused the Republic of Ireland boss of mind games after the Icelander urged the referee not to be influenced by the five-time Ballon d'Or winner.

Hallgrimsson had said that, in Portugal's win over the Republic of Ireland in October, Ronaldo - who had a penalty saved in that game - was "controlling the referee".

"He complimented me for putting pressure on the referee," said Hallgrimsson when asked about their touchline exchange, which ended with a handshake.

"It was his action on the pitch that cost him the red card. It had nothing to do with me - unless I got into his head."

Asked if he spoke to Ronaldo after the game, Hallgrimsson added: "No, I think we spoke enough when he came off.

"There was nothing to speak about. This was just a moment of a little silliness from him, I would say."

Perhaps unsurprisingly, Portugal boss Roberto Martinez held a different opinion of the incident, and having defended his captain, took a swipe at Hallgrimsson for speaking about the referee in the build-up.

"The red card is just a captain that has never been sent off before in 226 games - I think that just deserves credit - and today, I thought it was a bit harsh because he cares about the team," said Martinez.

"He was 60 minutes or 58 minutes in the box being grabbed, being pulled, being pushed and obviously when he tries to get away from the defender.

"I think the action looks worse than what it actually is, I don't think it's an elbow, I think it's a full body, but from where the camera is, it looks like an elbow. But we accept it.

"The only thing that leaves a bitter taste in my mouth is at the press conference yesterday, your coach was talking about the aspect of the referees being influenced, and then a big centre-half falls on the floor so dramatically at the turn of Cristiano's body."

Ronaldo could potentially miss the start of Portugal's World Cup campaign if they qualify.

While he is definitely suspended for Sunday's final qualifier against Armenia, he could receive a three-match ban for violent conduct.

In Fifa's disciplinary code, chapter two, Article 14(i) states: "Players and officials shall be suspended for misconduct as specified below... at least three matches or an appropriate period of time for assault, including elbowing, punching, kicking, biting, spitting or hitting an opponent or a person other than a match official".

If Ronaldo is hit with a three-match ban and Portugal qualify automatically, he will miss their first two group games in North America next summer.

However, if Portugal drop into the play-offs, Ronaldo will serve his suspension during those games.

His fate will be decided by a disciplinary committee, but whether or not his potential World Cup swansong is impacted, it was a hugely dramatic return to Dublin for the superstar.