NSW Waratahs' hopes of claiming an early Kiwi scalp at AAMI Park were brought undone by some dumb rugby, with the Chiefs capitalising to bank a 51-27 Super Rugby Pacific victory.

Skipper Jake Gordon did his best to drag his team to an unlikely victory, scoring two tries as they fought back strongly, but a horror opening 20 minutes proved telling for the courageous Tahs.

Prop Angus Bell was sent off for an alleged dangerous tackle two minutes into the match and then they were down to 13 men when centre Jamie Roberts got a yellow card for a deliberate knockdown.

The Waratahs weren't helped by a horror injury toll, losing fullback Will Harrison to a likely season-ending knee injury, while hooker Dave Porecki and his back-up Tom Horton both suffered head knocks which meant uncontested scrums for the final 35 minutes.

For the Chiefs winger Jonah Lowe bagged four tries among their haul of seven.

Waratahs coach Darren Coleman didn't want to use the cards as excuses.

"I'd prefer not to sort of make excuses around that," he said. "The difference between us and Kiwis at the moment, is that last 15 to 20 minutes and that's the biggest thing we need to improve.

"I'm proud of their fight and their character but we've got to get better in the last 20 minutes and that's the next progression for us as a team."

The teams were the first out onto Melbourne's AAMI Park for Super Round, which features five games at the venue over the weekend as the competition moves into its trans-Tasman clashes.

Unfortunately for the Waratahs they gave themselves too big a hill to climb with Bell marched soon after the opening whistle.

At almost the same time they also lost Porecki, who failed a HIA.

After an early penalty the Chiefs got their first try through hooker Samisoni Taukei'aho after they mauled the ball across the line.

Roberts got his 14th-minute yellow card as he clumsily attempted an intercept and while he was off Lowe and Quinn Tupaea both crossed for tries for the Chiefs as they raced to a 22-3 lead.

That was 30-17 by halftime with Gordon scoring the first of his tries after a handy break by lock Jed Holloway.

Tupaea also grabbed a second before Alex Newsome scored to give NSW the last say of the half.

Horton followed Porecki off the field after 45 minutes leaving the Waratahs without a line-out thrower with even Gordon having a go.

The halfback's second try closed the gap to just three points at the 50-minute mark when he intercepted a Bryn Gatland pass and raced 70 metres to touch down.

But the Chiefs countered soon later with Lowe taking an intercept of his own.

He then added another two tries, with the last coming in the final minute.

In the corresponding match of last year's trans-Tasman the Waratahs went down 40-7 and Chiefs skipper Sam Cane said he could see a notable improvement.

"They didn't help themselves with the discipline in the first 20 minutes when they got down to 13 men," Cane said. "To their credit they fought back really well, with a couple of probably soft lapses on our behalf which let them back in, but right up until probably that last 10 minutes or so the game was even there for the taking.

"I thought we played pretty well for the full 80 and to come away with with a good win and a bonus point was pretty important."