Ruby Walsh opted to partner Kemboy of Mullins' three runners and his decision was justified as the seven-year-old proved too good for his Cheltenham Gold Cup-winning stablemate in the Grade One feature.
Kemboy came unstuck at the first fence at Cheltenham as Al Boum Photo claimed the blue riband, but he gained compensation under a positive ride from Walsh.
British raider Definitly Red disputed the early lead with the eventual winner, but it was a duel between the Mullins' runners turning for home, with Al Boum Photo unable to go with Kemboy, who ran out a two-length victor.
Thrilling finish to the Punchestown Gold Cup, as KEMBOY gets the better of Al Boum Photo, in what proved to be a brilliant battle between the @WillieMullinsNH stablemates at @punchestownrace!— TimeformLive (@TimeformLive) May 1, 2019
There was a further 22 lengths back to the The Storyteller in third.
Walsh said: "He jumped really well. He quickened and quickened and quickened - he has pace and stamina and has a real knack of jumping."