The Munstermen have lost on their previous four visits to Leinster - their last win coming at old Lansdowne Road in the semi-final of the European Cup in 2006.
Munster beat Leinster 19-15 at Thomond Park earlier in the season and are going for a first regular season double over their fiercest rivals since 2008/09.
But O'Mahony insists they will need to be at the top of their game.
"I think there's a huge amount of pressure on both teams. I think it's a huge week for both," O'Mahony told the Irish Times.
"There's a huge amount at stake (on Saturday). They've an unbelievable quality of player. They've a great coach, they've had a great coach over the last couple of years, they believe in their game plan; everything that makes a great European team, they have. It wouldn't take a rocket scientist to know what makes them so good.
"It will take a huge collective performance, and that's when we're at our best. When we're firing as a forward pack and we're getting good ball to the backs.
"You've seen it this year probably in glimpses and some very good performances, but this is the biggest Rabo game of the year."
Head coach Rob Penney has made ten changes to the Munster side that beat Treviso last week with O'Mahony, Paul O'Connell, Conor Murray and Tommy O'Donnell all returning after Ireland duty.
Ian Keatley is also back while Denis Hurley comes in to partner Casey Laulala in the centres.
Simon Zebo is named on the left wing with props Dave Kilcoyne and BJ Botha both drafted into the side to join hooker Damien Varley in the front-row.
Leinster have niggling injuries disrupting their front row with Cian Healy a casualty.
Jack McGrath, Marty Moore and Tadhg Furlong are also missing, but the front row is still made up of full internationals with Michael Bent, Richardt Strauss and Mike Ross selected.
Jamie Heaslip is back to captain the side from No.8 while Gordon D'Arcy and Brian O'Driscoll continue their record-breaking centre partnership.
Rob Kearney returns to fill the full-back slot, with Zane Kirchner on the bench, and he will be looking to maintain his side's impressive form.
Leinster have won their last nine matches in all tournaments and have dropped only two points out of a possible 30 in their last six RaboDirect PRO12 fixtures.
But coach Matt O'Connor admits this will be a huge test.
"We know that we have to be really, really good. That's the bottom line," O'Connor told the Irish Examiner."We understand how important this [Munster game] is."
At Aviva Stadium, 7pm. Live on TG4
Referee: Alain Rolland
Assistant Referees: David Wilkinson, Michael Black (both IRFU)
Citing Commissioner: Peter Ferguson (IRFU)
TMO: Simon McDowell (IRFU)
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