Having firmly established himself as a starting flanker for South Africa, Erasmus joined the Cats ahead of the 1998 Super 12 season, where he continued to ply his trade until 2001. He was captain between 1999 and 2000, which saw the Cats make the 2000 Super 12 season semi-finals, only to lose to the Brumbies 28–5. In 2001, he was controversially stripped of his captaincy during season by coach Laurie Mains. Despite making the semi-finals again that season, both Erasmus and Mains departed the club at the end of the season, with reports citing their relationship one of the reasons.