De Bruin stepped up from his role as assistant following Johan Ackermann’s move to Gloucester and watched his side come out on top in a great battle at Ellis Park.
Sbu Nkosi’s try just after the interval reduced the deficit to only two points, but Mapoe helped himself to a double and Kwagga Smith added a fourth Lions try following Makazole Mapimpi’s five-pointer for the visitors.
Stormers also began their campaign with a victory, seeing off Jaguares 28-20 in the heat at Newlands.
Jaguares made a good fist of it, Emiliano Boffelli dotting down before a penalty try cut the gap to only five points, but they were denied a losing bonus point by Damian Willemse’s third penalty right at the end.
Sign up to our mailing list here and we’ll keep you up to the minute with weekly updates from the world of rugby.