Kei Nishikori and Yuichi Sugita beat Artem Smirnov and Sergiy Stakhovsky 6-3, 6-0, 6-3 as Japan won their Davis Cup World Group play-off after taking an unassailable 3-0 lead against Ukraine in Osaka on Saturday.
The Japanese duo completely dominated the contest, as they converted nine of 15 break-point opportunities, and the victory followed on from singles wins for Yoshihito Nishioka and Taro Daniel on Friday.
With the win, Japan secured its place in the World Group in 2017.
Australia, meanwhile, also returned to the World Group after they comfortably saw off the challenge of Slovakia in Sydney.
Doubles pair Sam Groth and John Peers were made to work hard against Andrej Martin and Igor Zelenay but eventually prevailed 6-4, 6-2, 6-7 (3-7), 7-6 (7-2) to earn Australia an unassailable 3-0 lead heading into the reverse singles matches on Sunday.
Australia were beaten by the USA to drop out of the world group in March but Nick Kyrgios and Bernard Tomic got them off to a strong start after respective singles wins on Friday and Groth and Peers did the rest to wrap up the triumph.
Elsewhere, New Zealand assured their place in Group One of the Davis Cup after they built up an unassailable 3-0 lead over Pakistan in their Asia-Oceania relegation tie in Christchurch, comfortably claiming Saturday's doubles contest.
New Zealand's Rio Olympic combination of Michael Venus and Marcus Daniell needed just one hour and 14 minutes to thump Pakistan duo, Aqeel Khan and Mohammad Abid Ali Khan Akbar, 6-0, 6-1, 6-2.