Osaka - Japan capped their return to the Davis Cup's elite World Group by completing a 5-0 home whitewash of Ukraine on Sunday.
World number five Kei Nishikori was rested for the two dead rubbers on the final day, as on day one, leaving Taro Daniel and Yoshihito Nishioka to put the finishing touches to a one-sided World Group playoff in Osaka.
Daniel beat Artem Smirnov 3-6, 7-5, 6-1 after rain had delayed the start of play and Nishioka thrashed Danylo Kalenichenko 6-2, 6-2.
Nishikori, who won Olympic bronze in Rio before reaching the semi-finals of the US Open earlier this month, heaped praise on his supporting cast.
"Our two young guys made a big jump in beating two tough guys," he said, referring to Friday's key victories over Sergiy Stakhovsky and Illya Marchenko, the world number 50.
"Sergiy has a lot of experience and Marchenko made the last 16 at the US Open, so they played some really good tennis to beat them."
Japan team captain Minoru Ueda stressed the importance of retaining a place at the Davis Cup's top table after inflicting a fourth successive play-off loss on Ukraine.
"At the moment, Nishikori is the only world-class player we have in Japan," he said.
"The other three have just reached the grand slam level, so they need to boost their rankings and being in the World Group in the Davis Cup will be a big help."