Japan fought back from 2-1 down to beat Britain 3-2 in their Davis Cup qualifier on Saturday to advance to the second round while the United States sealed a 4-0 victory over Taiwan.
With the score tied at 1-1 after Friday's singles rubbers, Britain's Joe Salisbury and Neal Skupski beat Japanese duo Yosuke Watanuki and Takeru Yuzuki 7-6(4) 7-6(3) in the doubles to move within one victory of the next round.
But Yoshihito Nishioka levelled the score with a 6-3 7-6(0) win over Jacob Fearnley before Kei Nishikori, a former world No 4, got the better of Billy Harris with a 6-2 6-3 win.
Nishikori had lost to Fearnley in straight sets on Friday but this time the former US Open finalist wrapped up the tie in 73 minutes for the 300th hardcourt win of his career as Japan beat Britain for the first time.
"I had a bad day yesterday. I tried to be more solid and aggressive and stay calm today," said the 35-year-old Nishikori, who was part of the team that lost to Britain in 2016.
"Very happy that the team won. This win will give us confidence. Our goal is to get to the main draw (Finals)."
Britain's Davis Cup captain Leon Smith congratulated Japan and praised their team's depth.
"You've got Nishioka who's been top 25, Nishikori has been No 4 in the ATP rankings," Smith said.
"So there's a lot of quality and we pushed them hard. We wish Team Japan all the very best for the rest of this year as well."
The US were 2-0 up against Taiwan after Friday's rubbers in Taipei City and sealed the tie when Olympic silver medallists Austin Krajicek and Rajeev Ram beat Ray Ho and Wu Tung-Lin 6-4 7-6(4) to set up their first home tie in three years.
Mackenzie McDonald then beat Huang Tsung-Hao 6-2 6-3 as the Americans' experience shone through and they won 4-0 without dropping serve even once in the tie.
"Fortunately we were able to finish the job in the first match. We took care of our serve really well," Krajicek said.
The US will play the Czech Republic in the second round in September after the European side beat South Korea in the doubles rubber to take a 3-0 lead.
The first round of the Davis Cup has 26 teams playing for a place in September's second round of qualifiers.
Last year's runners-up, the Netherlands, will join the competition in the second round which will consist of seven ties in a battle to make November's Final 8 alongside hosts Italy.