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.
Lions, led by fit-again captain Warren Whiteley, saw it out, Elton Jantjies not having the best of days from the tee, but landing three conversions for the 2016 and 2017 runners-up.
Stormers also began their campaign with a victory, seeing off Jaguares 28-20 in the heat at Newlands.
Tries from Damian de Allende, Siya Kolisi and debutant Raymond Rhule gave the Cape Town franchise a 22-6 lead early in the second half.
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.
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