Waratahs coach Michael Cheika spat the dummy over a refereeing decision in his team's 31-26 win over the Rebels on Friday.

Despite the win, which saw the Tahs retain their unbeaten run over their Melbourne-based rivals, Cheika voiced his disappointment about the carding of hooker Tatafu Polota-Nau in the 24th minute - for repeated infringements at the breakdown.

Referee Rohan Hoffman had issued a team warning to Tahs captain Dave Dennis about the home team's tactics.

Cheika disagreed with the match official's call.

"I was really disappointed about the yellow card from the referee, because it [was] a collapsed maul and the player doesn't have to go anywhere," Cheika told the Sydney Morning Herald.

"But I understand it's also Rohan's first game of Super Rugby so, like anyone else, [he is] getting acclimatised."

Assistant coach Daryl Gibson had a different view, suggesting the Waratahs were getting it wrong at the breakdown and said they needed to be more mindful of the power of interpretation in the highly contested contact area.

"The Australian teams are very competitive at the breakdown and that's something referees are going to have come up to speed with," Gibson told the SMH.

"The Reds, Brumbies and Waratahs are all very competitive around that area and are putting the refs under pressure to get that right."