The Munster back rower has made a swift transition from underage to senior international rugby, having debuted as a replacement for Sean O'Brien during the Six Nations win over Italy last February.
Appearances against New Zealand and more recently South Africa have battle hardened the 23-year-old, who is relishing this latest opportunity to test himself against another Rugby Championship outfit - Argentina.
The video analysis has shown O'Mahony that the South Americans remain a strong outfit up front, but they look a more 'rounded team' in recent months.
"It's going to be physical. Argentina have a big pack, they've a world class back row...(Juan Manuel) Leguizamon and (Juan Martin) Fernandez Lobbe. Their maul is very dangerous and they've a good lineout," said O'Mahony.
"As a 15 we're going to have to front up, everyone. They're a very potent side. Since they've got into the Rugby Championship they have really improved. Even in its first year, they've come on in leaps and bounds and it's really helped them.
"They haven't gone away from that physical team they were - what they are known for being good at - but they've added other things and it's made them more of a rounded team."
Commanding the breakdown is a key focus for the Corkman and his back row colleagues this week, knowing how decisive an area it could be what is expected to a tight game.
"The breakdown is where international games are won these days and that's where we are going to be focusing on. Not just 1 to 8, not just the pack, it's a backs issue now as much as a forwards one.
"We're just going to look for a physical performance from 1 to 15. I keep bringing up their back row but as a 15, they are accurate and that's what you want at a breakdown.
"But we'll be focusing on ourselves, looking for opportunities to do better than they do there."
Saturday's Test is the sort of match O'Mahony would have dreamed about playing in when he progressing through the underage ranks at Cork Constitution.
A son of Cork Con stalwart John O'Mahony, Peter was just five years of age when he was thrown in with the club's Under-8s. It was a tough, tearful start, but his love of the game quickly developed.
The Munster Academy graduate has since become one of the youngest captains in provincial rugby, leading the Munster senior team on occasion in the past year after becoming a recognised leader in the Ireland underage set-ups.
Three of that year's Irish U-20 team are part of the GUINNESS Series squad - namely O'Mahony, Conor Murray and Rhys Ruddock - and the strong-willed Corkman is enjoying the current mix of young and old.
"Every team goes through a stage where younger guys come in and are knocking on the door," added O'Mahony, who said the performance of the Ireland XV against Fiji last Saturday was 'a joy to watch'.
"We're lucky enough to have a big group coming through at once. I think it's given everyone a lift, even the older fellas are getting a kick and a buzz out of the younger fellas being around and adding their two cents to training.
"When new guys come in, it brings a different perspective to things. Rugby is always evolving and to have guys who see things differently is great for everyone.
"I'm sure Declan is learning off some of the young fellas as much as Donners (Donncha O'Callaghan) is and Rog (Ronan O'Gara) and Jamie (Heaslip) and the guys who have loads of caps."
O'Mahony has welcomed the increasing competition for back row places, with 20-year-old Ulsterman Iain Henderson impressing in the number 6 jersey against Fiji.
"It's great for everyone to have that level of competition, everyone wants to win in a Test jersey and they push each other on.
"And that Fiji performance, it was really positive. The lads playing really gave everyone in the squad a lift," he admitted.
It may have been a non-cap international but the 53-0 success at Thomond Park got Ireland back on the winning trail at senior level, following five successive defeats.
Wrapping up 2012 with a final victory over Argentina is hugely important not just for morale, but also given the Ireland's seventh place ranking and the fast-approaching 2015 Rugby World Cup draw.
O'Mahony will turn 26 the day before England 2015 is scheduled to begin. Featuring in that tournament is undoubtedly on his list of goals, and ensuring Ireland's place in the second band of seeds for the pool allocation draw would be the best possible start.
The steely ambition shines through when he says: "Those past achievements (Grand Slam and World Cup wins), they are huge for a nation, but as a group of players we are talking about creating our own legacy.
"There are fellas there that have won a Grand Slam, but a lot of us here weren't involved in that squad so we are trying to go down our own path."