In a scrappy affair, punctuated by 26 penalties and endless knock-ons, the Rebels claimed their first victory of the new competition thanks largely to the class and boot of five-eighth Matt Toomua.

Toomua slotted five penalty goals and two conversions for a 19-point haul as the Rebels, despite being homeless due to Victoria's coronavirus outbreak, completed their first season double over NSW.

"Pup (Toomua) is a great character, he's a great leader leading us around and obviously a great strategist. He's a cool head and he's doing a great job at the moment," said Rebels captain Dane Haylett-Petty.

Dave Wessels' men trumped the Tahs 24-10 before the suspension of Super Rugby proper in March. Friday night's triumph marks the first time in the franchise's 10-year existence they have toppled their NSW rivals twice in a season.

But the milestone victory at the SCG was anything but pretty.

The Rebels, who lost Haylett-Petty to a first-half knee injury, butchered a series of try-scoring opportunities before 2019 John Eales Medallist Marika Koroibete finally sealed the win four minutes from fulltime.

With the exception of Alex Newsome's seventh-minute try, a 25-metre intercept effort off an errant Reece Hodge pass, the Waratahs, starved of possession and territory, never looked like scoring.

Leading 12-10 courtesy of four Toomua penalties, the Rebels extended their lead to nine points in the shadows of halftime.

With the Waratahs down to 14 men after Wallabies captain Michael Hooper was yellow-carded for a second offside offence, Rebels halfback Ryan Louwrens crashed over from the scrum base and Toomua converted to make it 19-10 at the break.

It was not until half-an-hour into the second stanza that the next points came and, typically, they arrived via Toomua as the Waratahs' ill-discipline continued to cost them.

All up, they conceded 17 penalties and Penney and captain Rob Simmons were at a loss to explain why the Waratahs could be so poor after being so good in last week's gallant one-point loss to the Brumbies.

"We weren't there where we needed to be emotionally and the Rebels taught us a lesson," Penney said.

Simmons, who revealed after the match that he had suffered broken ribs that will sideline him for several weeks, said the Waratahs "lost it before the game even started".

One of the few positives for the Waratahs was the long-awaited return of halfback Jake Gordon.

In his first game back since before COVID-19, Gordon was introduced early in the second half and made a successful return from a nagging hamstring injury.

Australian Associated Press