The respectives captains and coaches met up with each other at Mizuho Sports Park in Nagoya for a media launch, three days before the opening matches in Pool A.
Both sides know the importance of making a winning start to a competition. O'Mahony and his team-mates achieved just that in the 2009 RBS Under-20 6 Nations in February with a gutsy 9-6 defeat of France in Athlone.
Ireland's second place finish in the Six Nations has boosted confidence for the journey to Japan and talented back rower O'Mahony is looking forward to getting the JWC underway on Friday.
"This is my first World Championship and I'm really looking forward to it," he told IrishRugby.ie.
"We've drawn a very physical group but as our coach Allen Clarke has said, we're not looking past Argentina at the moment.
"I've seen some of their stuff from last year. They're a very physical side, they've a big pack and are well able to throw the ball about.
"They're going to be a very tough team to beat. I know the lads struggled last year against them and I can't see it being much different this time around. But we're quietly confident."
O'Mahony, who has been playing for Cork Constitution since he was five years of age, and Clarke, the former Ulster and Ireland hooker, both highlighted what a 'great group of lads' they are working with in the Under-20 set-up.
Clarke's management team includes experienced manager Phil Orr and assistant coaches Nigel Carolan and Colin McEntee.
The Irish players and management arrived in Nagoya on Monday and have been acclimatising to the humid conditions, with temperatures expected to rise towards 30 degrees celsius at the weekend.
Competition for places has intensified with the inclusion of some Under-20 Development players who did not feature in the recent Six Nations, with Ballynahinch flyer Nevin Spence perhaps being the most well-known of them.
Looking forward to building on the four wins in the Six Nations, Clarke said: "Our success in the Six Nations was built on an ethic of hard work, good attitude and a tremendous spirit within the team.
"We won a lot of close games, three stand out, and that in itself tells you when you come out the other end that you've got something special to work with."
Commenting on Friday's opponents, he added: "I've watched Argentina on video. They're certainly a physical side and like all Argentinian sides, they're going to challenge you around the fringes. But they've got the flair too.
"They've got their age grade programmes up and running now. They're probably a nation that mature slightly earlier than the Irish.
"Obviously the first game is our focus at the moment. But it's only one game of three in our pool stages and one game of five in the whole tournament.
"From a player's point of view, what a wonderful experience and opportunity to test tourself?
"From the team's point of view, let's see how we've progressed from the Six Nations and from a national point of view let's benchmark the quality of our players to those throughout the world."
Ireland's other games in Pool A are against defending champions New Zealand next Tuesday (7pm local time/11am Irish time) and tournament newcomers Uruguay on Saturday week (June 13) (1pm local time/5am Irish time). Both fixtures are at Mizuho Sports Park.
Meanwhile, the International Rugby Board has announced a new format for the IRB Junior World Championship from 2010 onwards, with the number of participating teams being reduced from 16 to 12.
This restructure, approved by the IRB Council, means that the top 12 teams at this year's IRB TOSHIBA Junior World Championship in Japan will automatically qualify for the 2010 tournament in Argentina.
The bottom four will participate in regional qualifying structures for the second-tier IRB Junior World Rugby Trophy in 2010.
"The IRB is committed to increasing the overall competitiveness of the game and our age grade tournament strategy is very important in achieving this," said IRB Head of Development and Performance Mark Egan.
"The IRB Junior World Championship has proven extremely successful in providing the next generation of international players with a platform to develop their skills in a format that replicates a Rugby World Cup environment.
"However, with 550 players and team staff, the tournament is also a large one and in the current economic climate it is prudent to take measures to relieve the financial pressure on both the IRB and the hosting Union, while maintaining the high standard of the tournament.
"The new format for the IRB Junior World Championship will optimise the opportunity for competitive pools matches, while the regional qualifying tournaments and IRB Junior World Rugby Trophy will continue to provide a strong global age grade player development pathway."
The new tournament structure will comprise three pools of four teams with the winner of each progressing to the semi-finals, along with the best placed runners-up.
The remaining teams will play for a positional ranking. Unions were notified of the structural change last month.