Australia coach Joe Schmidt said he may be forced to call on reinforcements for their European tour after losing two players to injury in Saturday's nervy 19-15 win over Japan.
The Wallabies survived a second-half comeback to beat Eddie Jones's team in a wet Tokyo and get their five-test tour off to a winning start.
The victory came at a cost, with locks Lukhan Salakaia-Loto and Josh Canham both going off injured within the opening 20 minutes.
Australia now travel to Europe to face England, Italy, Ireland and France on successive weekends.
Schmidt said the injuries "made it very difficult to get some combinations going" and admitted he would need to find solutions before playing England at Twickenham next week.
"It just means that we are light in the second row and we may need to get some reserves dug out from Australia," said the coach.
"Josh Canham obviously won't be available next week and as yet I don't have any feedback on Lukhan."
Australia fielded an unfamiliar line-up with 13 changes and a new captain in Nick Champion de Crespigny, who was winning only his third cap.
The new skipper scored the opening try before Josh Flook added another with the Wallabies looking comfortable despite the wet and chilly conditions.
Japan fought back after halftime.
Tries from Shuhei Takeuchi and Australia-born Ben Gunter, either side of a Carlo Tizzano score, brought the hosts within sight of a first win over the Wallabies.
Schmidt said the finale did not need to "be that tense" but praised his team for how they dealt with the conditions.
"Both teams were very keen to play fast but it was very hard to play fast because it was very damp," he said.
"Both teams started to threaten but lost the ball. It meant that we had to be more direct."
JAPAN LIKE 'SPECTATORS'
Japan were cheered on by over 40 000 fans at Tokyo's National Stadium but could not get the win over the line after a slow start.
Former Wallabies coach Jones said his players were "like spectators" in the first half and challenged them to reproduce their second-half performance for the full 80 minutes.
"Disappointed that we weren't able to find the best version of ourselves, in the first 30 minutes particularly," said the Australian, who left the Wallabies two years ago under a cloud to take up the Japan post.
"But what I am super pleased about is that now we are a team that stays in the fight."
Salakaia-Loto lasted just seven minutes before he left the field following a heavy hit.
His replacement Canham went back off again just over 10 minutes later to undergo a head injury assessment.
The injuries did little to disrupt the Wallabies' rhythm and Champion de Crespigny pounced for their opening try in the 13th minute.
Flook scored another on the half-hour mark, cantering over the line after Andrew Kellaway cut through the Japan defence.
Japan looked livelier in the second half and Takeuchi scored their first try in the 52nd minute after a period of pressure.
Australia hit back five minutes later when Tizzano rumbled over but Gunter set up a nerve-jangling finish when he cut the deficit to four points with 20 minutes remaining.
Champion de Crespigny said there were "some moments that we let slip" but vowed that the Wallabies would be ready to face England.
"A really tight contest in some tough conditions," he said.
"Full respect to Japan, we knew they were going to be a quality side and they definitely proved that today."
Japan also head to Europe and will face world champions South Africa at Wembley before playing Ireland, Wales and Georgia.
