But five unanswered tries made the final score 42-17 to Gareth Jenkins's team and Thomas knows the only way to beat the world-class Aussies is to play at a high tempo.
WRU Audio: Jonathan Thomas calls for intensity and tempo against Australia
"Huge positives can come out of that second half and the intensity and tempo we played in that second half we will be looking play with for the full 80 minutes against Australia."
"Every game is pressure in the World Cup. This is the game, deep down, fans players and management have secretly had one eye on. This game could decide the group and we have to come out and play like a world class side."
As Thomas says, every game at this level brings with it its own pressures and the opening match against Canada proved a tough test.
"I think all week we said Canada would come out all guns blazing and they certainly did that. They certainly played like players who were out to prove to a point and they played some excellent stuff," Thomas told www.wru.co.uk.
Thomas went on to explain how Wales turned around the 12-9 half-time deficit. He said, "Our composure in the second half was great and Canada tired as the game went on, we exposed that.
"We have huge belief in the squad and even though a lot of fans might have been panicking at half time we have confidence as a group. We said to ourselves not to panic, to stick what we know and to go through the phases in the second half.
"I thought the subs were excellent in the second half. They came on and made a huge impact and we played well in the last 20 minutes," he concluded.