But the veteran halfback let out a massive sigh of relief as the Wallabies held on for a 15-6 win against Wales on Saturday night (Sunday morning AEDT) despite being forced to play for 10 minutes with only 13 players.

Genia and lock Dean Mumm were sent to the sin bin in a game-changing 10 minutes that gave Wales an opportunity to snap a 10-game losing streak against Australia.

But somehow the Wallabies managed to hang on and Genia could walk away a relieved man, satisfied he made the right call to tackle Gareth Davies from an offside decision. Davies took a quick tap with Wales surging, and Genia admits he deliberately made the cynical foul to save a try for his team.

"I was pretty gutted to be honest," Genia said. "I felt like I really let the boys down in terms of being off for that 10-minute period. But it was one of those ones where I felt like if I didn't make the tackle, he would have scored.

"I knew that it would be cynical, but I also didn't want to give them five points by letting them score that try. The guys dug in with an incredible effort. It's one of those ones where you make a decision based on how you feel and while I did get yellow-carded, I felt like I made the right call."

Genia's absence was compounded moments later when Mumm was penalised for grabbing a Welsh lineout jumper in the air and he was sent to the sin bin.

The Wallabies were also dealing with injuries to David Pocock, Israel Folau and Matt Giteau. They rallied and made try-saving tackles to protect their line as Genia and Mumm sat anxiously on the sideline.

The scrum was also able to stay strong when they were one-man down at the set piece and Wales had multiple chances to push them backwards close to the line.

Genia described it as one of the "sweetest" wins of his international career. "I think it's just a credit to the players in terms of wanting to build a certain culture. A lot of it is about not letting your teammates down and working hard for each other and having that respect for one and other," Genia said.

"Those sort of things really come out when you're under the pump. You could see guys busting their backsides to make sure they were on their defensive line, making sure they were chopping low, not allowing them to get that go forward, the rolling mauls, the scrum defence.

"It was just an incredible effort and it's one of the sweetest victories I've been a part of. It made it pretty tough and guys just hung in there."

The Wallabies will play Scotland in the quarter-final at Twickenham next weekend and will avoid South Africa and New Zealand until a potential meeting in the final.

They are nursing battered bodies after being forced to withstand a Welsh onslaught.

Kane

Douglas had his best game since returning to the Wallabies jersey, making 15 tackles in a massive effort.

"You find that self-belief in all those training sessions we do. You have to find it, we were in a tough situation there and it was good getting out of it," Douglas said.

"I don't think I've been involved in a defensive effort like that, it was pretty tough. But there will probably be more like it coming.

"I think it will help us massively, as far as we go we can look back on that passage [when we were down to 15 men]. But there are a lot of improvements as well."