Rees-Zammit suffered a toe injury in his fourth game for the Bears, but proved his fitness to earn selection on Wales’ bench for the autumn opener.
That led to plenty of pre-match focus being on a replacement and he got some of the biggest cheers of the afternoon.
Wales might have suffered a heavy loss, but the wing was still able to reflect on being in his “happy place” in a social media post.
“It was a great experience,” he said. “I did really miss being able to play at the Principality Stadium in front of our fans.
“It was incredible. You don’t really know you’ve left until you go back. When I came on and heard the crowd – all the support I had, it meant so much to me.”
Wales won just one of 19 Tests while Rees-Zammit was out of the picture in America, but the wing is confident of brighter times under Tandy.
“You could see glimpses last weekend of what’s to come. That was building a foundation of where we want to be and what team we want to be,” he said.
“We can do as much as we can in training, but we’ve got to show it on the weekend when all the fans have paid good money to come watch us play. It’s what they deserve.”
Rees-Zammit’s last international victory was against Georgia at the 2023 World Cup and he intends to help Wales repeat their summer success against Japan in a vital game ahead of December’s World Cup draw.
Eddie Jones’ Brave Blossoms would leapfrog Tandy’s side into 12th in the world rankings if they upset the odds in Cardiff.
Rees-Zammit said: “Everyone’s locked in on what’s next. Japan will be a tough game, but everyone is raring to go and is buying in 100%. We’re all ready.”