Waratahs coach Dan McKellar returns to his old club Brumbies on Saturday and has a message for his team: "Front up."

The 'Tahs crashed to their first defeat of the Super Rugby season last weekend against the Reds in Brisbane, losing 35-15, and McKellar wants an immediate reaction in Sydney.

"There aren't many changes in the group this week, which means those selected have the opportunity to front up with an edge and show a response," he said.

"It's a big derby game. The New South Wales boys want to knock off their arch-rivals, and that's the Brumbies.

"I spent many years in that camp, but now I'm here, and I'm driven and energised to do all I can to turn things around."

McKellar coached the Brumbies from 2018 to 2022 before resigning to take over at English Premiership team Leicester Tigers.

But he only lasted a year before being axed, moving to the 'Tahs this season.

'RIVALRY STRONG AS EVER'

While the Canberra-based Brumbies have historically dominated the fixture in recent years, McKellar insisted the rivalry was as strong as ever.

"There's no chance this rivalry dies. Both teams are desperately hungry to beat each other," he said.

"It goes back a long way, and it's part of what makes Australian rugby great."

The Brumbies, with three wins from five so far, head into the game boosted by the return of Wallabies No 8 Rob Valetini, who had been sidelined by a hamstring injury suffered pre-season.

"It's a huge boost to have Rob back in our side," said Brumbies coach Stephen Larkham, who took over when McKellar left.

"He's a world-class back row who possesses so many qualities that help our team."

The Brumbies are coming off a 38-21 victory over Fijian Drua last week and are aiming to pile more misery on the Waratahs.

"We're looking forward to taking on the Waratahs in their own backyard. They've made a strong start to the season despite their slip-up against the Reds last weekend," Larkham said.

"Everyone at the club wants to play in these sorts of matches against our biggest rivals."