O'Brien crossed for two tries in the opening half, while Osborne added Leinster's fifth try late in the game to round off a comfortable bonus-point victory.
Kildare's Jimmy O'Brien, Jamie Osborne, and Sam Prendergast all played key roles as Leinster defeated Cardiff 29-5 at the newly redeveloped RDS on Saturday evening.
O'Brien crossed for two tries in the opening half, while Osborne added Leinster's fifth try late in the game to round off a comfortable bonus-point victory.
Prendergast also impressed at out-half, creating opportunities throughout the match and setting up tries for both O'Brien and Osborne, although he converted just two of his five attempts.
Hugo Keenan and Jack Conan were also on the scoresheet as Leinster secured their first United Rugby Championship victory of the season, following two defeats in South Africa.
The defending champions now turn their attention to next weekend's Champions Cup opener against Clermont Auvergne.

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