The Bulls beat the Sunwolves 34-21 in Super Rugby but made it hard for themselves against the strugglers from Japan when flanker Renaldo Bothma was sent off for a high tackle in the opening minute of the second half.
The Bulls, three-time champions, collected their first win of the season but missed out on a bonus point ahead of a two-match tour of New Zealand to play the Chiefs and Blues.
In Pretoria, the Bulls led the Sunwolves 17-14 at halftime after winger Kenki Fukuoka's sizzling run down the left to score in the corner for the visitors just before the break.
Bothma caught Sunwolves captain Ed Quirk with a forearm to the head straight from the second-half kickoff and was given a red card, leaving the Bulls up against it.
They toughed it out, scoring two tries through centre Jan Serfontein - his second of the game - and lock Jason Jenkins.
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Sunwolves replacement Liaki Moli had a try disallowed in the last seconds, after it was initially awarded, and the conversion was taken and missed; before referee Jamie Nutbrown was advised by television match official Mike Vos to review whether Moli had control of the ball when he went over the line. He didn't.
Despite the win the Bulls, whose last Super Rugby title was in 2010, are sixth of the eight-teams in South African group standings.
