Kei Nishikori and Yuichi Sugita beat Artem Smirnov and Sergiy Stakhovsky 6-3, 6-0, 6-3 as Japan won its Davis Cup World Group play-off 3-0 against Ukraine on Saturday.
The Japanese duo was in control from the outset and converted nine of 15 break point opportunities.
With the win, Japan secured its place in the World Group in 2017.
Yoshihito Nishioka and Taro Daniel gave Japan a commanding 2-0 lead with wins in singles on Friday.
Ukraine was bidding for its first appearance in the World Group but will remain in the Europe/Africa Zone Group 1 next year.
John Peers and Sam Groth clinched the Davis Cup World Group play-off tie for Australia with a doubles win over Slovakia in Sydney on Saturday.
Peers and Groth were taken to four sets by the Slovak pair of Andrej Martin and Igor Zelenay after holding a match point in the third set.
The duo went on to secure Australia's World Group status 3-0 in the 2017 Davis Cup competition with a 6-4, 6-2, 6-7 (3/7), 7-6 (7/2) victory in two hours and 21 minutes.
"So much depends on the draw but we're not there just to make up the numbers," captain Lleyton Hewitt said at the prospect of playing again in next year's World Group.
"We expect that we can go deep. This group wants to try and get our hands on the Davis Cup.
"It's been quite a while now since we've had an opportunity to play in a final and I know from experience I'd love these boys to have that experience of going out there and playing for Australia."
Teaming up for the first time in the competition, Peers and Groth were impregnable on serve, dropping only 18 points in 21 service games and did not face a break point.
They broke the Slovaks three times and looked to be steaming to a straight sets win until they had a match point at 5-6.
Slovakia then went on to take the third-set tiebreaker before a back hand put-away by Peers sealed the play-off tie for Australia in a fourth-set tiebreaker.
It was Peers's first win for Australia after losing his only other rubber — a doubles match alongside current captain Hewitt against the United States in March.
The 'dead' reverse singles will be played on Sunday.
Australia only needed one more win after Nick Kyrgios and Bernard Tomic won their opening day singles in straight sets on Friday.
The 15th-ranked Kyrgios shrugged off recent hip problems to whip through Martin 6-3, 6-2, 6-4 while the 21st-ranked Tomic completed a 7-6 (7/5), 6-4, 6-4 win over Jozef Kovalik.
Australia, who lost to the United States in this year's first round, will now extend their stay in the World Group to four years.
Slovakia, who came to Australia without their two leading stars -- 31-ranked Martin Klizan and 102-ranked Lukas Lacko -- have not been in the premier group for 10 years.