Peter Smyth's charges finished second in the table, three points behind title favourites Cork Constitution.
Speaking after his side's fourth straight league win and looking forward to facing Old Belvedere, Smyth said: "'Belvo are a very, very good side. Andy Dunne is an exceptional player, he's marshalling the back-line there so it's going to be tough (against them).
"To be honest with you, this is very much a 50-50 game. We have home advantage (at Templeville Road) but it's not going to bother them travelling three miles across the city for an away semi-final.
"And the thing is they have a huge winning culture from playing this year. They've won probably 85 or 90% of their games."
The last time the two sides met was in this season's Leinster Senior League Cup final which Mary's won 9-3 in a tightly-contested battle.
But Smyth, who has Australian Shaun McCarthy and former Leinster flanker Ciaran Potts at the coaching helm, suggested that the provincial cup decider could have easily gone the other way.
"In that match, we won 9-3 but they were very unlucky not to score a try. We got a penalty to close it out and we were six points ahead but they nearly scored twice at the death," he explained.
Smyth will also want to keep a close eye on the other semi-final between Cork Constitution and Dolphin.
"I still think Cork Con will be the team to beat for whoever wants to win the trophy, but I think with Old Belvedere and Mary's, it's a 50-50 game."
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