Andy Farrell expects World Rugby to review its rules after Ireland benefited from a “weird” law en route to blitzing depleted Italy 57-6 in the Guinness Six Nations.

The unfortunate Azzurri battled on two men down for three quarters of Sunday’s match in Dublin after substitute Hame Faiva was dismissed having just replaced fellow hooker Gianmarco Lucchesi due to injury.

Those premature departures led to uncontested scrums and, under governing body guidelines, necessitated the removal of a second Italian player, with number eight Toa Halafihi the man sacrificed.

Ireland took advantage by running in nine tries, including two apiece for outstanding debutant Michael Lowry and the returning James Lowe, to bounce back from defeat to France a fortnight ago.

Italy left the Aviva Stadium field with just 12 men due to Braam Steyn being sin-binned for the final five minutes, leaving Ireland head coach Farrell to reflect on a strange afternoon.

“There’s not many times we’ve played a Test match against 12 players, so there’s plenty we can take away from it,” he said.

“It’s just weird (the law). We understand why the rule was brought in but at the same time I suppose, in situations like that, occasions like that, it’ll bring the rule back to everyone’s attention and they’ll look at it.

“Rightly, Italy were trying to slow the game down, it’s what everyone would have done.

“When you’ve got uncontested scrums for so long in the game, everyone’s legs are nice and fresh and it’s the reason Italy were tenacious in defence, even when they went to 12 men.”

New Zealand-born Faiva was dismissed for making contact with the head of Dan Sheehan only 10 minutes after coming on for the stricken Lucchesi.

Ireland led 7-3 at that stage thanks to Joey Carbery converting his own try and Azzurri full-back Edoardo Padovani landing a long-range penalty.

Scores from Jamison Gibson-Park, stand-in skipper Peter O’Mahony, Ryan Baird and Kieran Treadwell, plus braces for Lowry and fit-again Lowe, secured a resounding bonus-point win, with Carbery and Johnny Sexton kicking four and eight points respectively.

The unusual victory moves Ireland second in table, three points adrift of the Grand Slam-chasing French.

After suffering defeat in Paris a fortnight ago, the Irish may be reliant on points difference to snatch the title and deputy skipper O’Mahony conceded they could have been more clinical.

“We want to be ruthless but we weren’t, certainly, in the last 20 minutes of the first half and parts of the second half,” he said.

“We weren’t accurate and we should have made life more difficult for a team that were down to 13 and 12 players at one stage.

“So you want to be ruthless, but at times our inaccuracy let us down.”

Electric Ulster full-back Lowry enjoyed an unforgettable afternoon and would surely have claimed a hat-trick but for his selflessness.

Farrell was delighted for the 23-year-old newcomer and said: “He was great. He was lively and he was as brave as we knew he was going to be.

“Getting the two tries and then making the space to get his third and then passing it on to his mate James Lowe in the corner typifies what Mikey’s all about.

“Everyone involved in the squad is absolutely made up for Mikey and his mum and his sister and his girlfriend – it’s a big day for them.”

Penalties from Padovani and Paolo Garbisi were scant consolation as Italy suffered their 100th Six Nations defeat and 35th in a row.

Azzurri head coach Kieran Crowley said: “On the team sheet, you must name two hookers, two loosehead props and two tighthead props.

“When you then lose two hookers, I was not prepared to go with props that have never hooked before into that position.

“There were two identified on the team sheet and, unfortunately, Lucchesi dislocate his elbow and then the red card occurs.

“We had to go down to 13; it’s something that we have no control over on the rules – they (World Rugby) have to look at that.”