Andrew Porter has described the key to his World Cup selection as "like writing with your bad hand".

The versatile prop knows he must flourish on both sides of the scrum in order to force his way into Ireland's final 31-man World Cup squad.

The 23-year-old made the testing transfer from loosehead to tighthead two years ago, with Leinster keen to capitalise on his raw power in the scrum cornerstone number three role.

Now an accomplished tighthead, he finds himself deputising in his old loosehead role, admitting only mastery of both will secure him a seat on the plane to Japan.

"I hadn't played at loosehead for about two years, so I was a bit rusty," said Porter, who featured in both prop roles during Ireland's 29-10 victory over Italy in Dublin on Saturday.

"But it's something I'll be looking to work on to be as versatile as I can.

"So I'll be looking to push that forward in the next few weeks.

"At the beginning, two years ago, switching from loosehead to tighthead was very tough. Moving across the scrum is like writing with your bad hand.

"But you're going up against some of the best guys in the world in training and in matches, so that's really helped over the last couple of years.

"And then it's the same again in the past few months, having time at loosehead again."

Joey Carbery bagged a try but limped out of the Aviva Stadium clash against Italy with ankle trouble, leaving the Munster fly-half a World Cup doubt.

Dave Kearney, Andrew Conway, Jordi Murphy and Kieran Marmion also crossed as an experimental Ireland team secured a routine victory over Conor O'Shea's Azzurri.

Maxime Mbanda and Carlo Canna bagged first-half tries as Italy exploited Ireland's pre-season ring-rustiness.

Porter admitted enjoying his twin tests on either side of the scrum, but insisted he still has plenty of hard graft ahead.

"The neck's a bit stiffer than usual after a game, but hopefully I can just keep getting more used to it again," said Porter.

"It's always been something coaches go over with me, that if needs be I could slot back in at loosehead.

"So it's important now to get reps in training, and have runs in games like these.

"It's great to be able to play both sides, it pushes my case a bit forward like that."

Head coach Joe Schmidt confirmed that Jack McGrath's half-time substitution was to allow Porter the chance for a run back at loosehead.

New Ulster recruit McGrath and Munster man Dave Kilcoyne are Ireland's specialist looseheads, with British and Irish Lions star Tadhg Furlong the main tighthead exponent.

Schmidt conceded that the flexibility for props to feature either side of the scrum becomes increasingly important when whittling numbers down to that final 31.

"We were really happy with Jack McGrath's first half to be honest," said Schmidt.

"He got off the line, made some good impact tackles. And Jack for us is very good around our attacking breakdown as well.

"But we wanted to shift Andrew Porter across and give him 20 minutes there.

"Because the reality is at the World Cup you're going to need at least one prop who can play either side, potentially maybe even two.

"John Ryan has played either side in the past, and Finlay Bealham has played either side.

"So those three will probably be the guys who could cover that role, then the others would be more specialist, the likes of Cian Healy, Jack McGrath and Dave Kilcoyne on the loosehead and Tadhg Furlong on the tight."