The Australian side hold a 15-0 lead at the break with two tries to Waratahs winger Taqele Naiyaravoro.
Rookie Highlanders winger Tevita Nabura was shown the red card after 18 minutes for dangerous play while Aaron Smith was sent to the bin with a yellow just two minutes later.
Nabura was judged to have kicked out at a player's face while jumping to collect a high kick.
The decision went to the video referee who ruled the action was deliberate.