Back to drawing board for Pumas
The Pumas have still not recorded a win in this year's Currie Cup Premier Division and will next play Western Province at Newlands on Saturday.
The Bulls outscored the Pumas by six tries to one as the Pretoria side dominated play up front.
However, Mentz admitted his side wasn't good enough to crack the Bulls' defence.
"We were definitely outplayed and outmuscled by the Bulls," said Mentz.
"We couldn't get one set piece of our own and we couldn't put their set piece under pressure, and that flowed through to the rest of our game.
"We tried hard at times and put some phases together, but on the night it was definitely not good enough,"
The Pumas are currently eighth on the standings after six rounds.