The reigning Super League champions dominated the opening period, leading 30-4 thanks to tries from debutant Tom Amone, Elliot Minchella, Joe Burgess, Oliver Gildart, and Peta Hiku.
Despite a late Broncos resurgence scoring four unanswered tries, Hull KR held on to become only the sixth English club to win the competition since 1987 and the first to hold all four major titles since 2007.