Rafael Nadal came back twice from a break down against Japan’s Yoshihito Nishioka to put Spain into the ATP Cup quarter-finals in Australia.
The world number one won 7-6 (7-4) 6-4) to give Spain an unassailable 2-0 lead in the tie after Robert Bautista Agut had earlier beaten Go Soeda 6-2 6-4.
Nadal then paired up with Pablo Carreno Busta to win the doubles rubber and end Japan’s chances of a last-eight spot.
Argentina later beat Croatia to advance.
Croatia could still book a place in the knockout stage if they win the remaining doubles rubber against Argentina, who sealed victory in the tie with straight-set wins for Guido Pella and Diego Schwartzman over Marin Cilic and Borna Coric respectively.
Spain, who won the Davis Cup in November, ended their group-stage campaign with a perfect record of nine wins.
But an unusually sluggish Nadal was made to work hard against world number 72 Nishioka, making 19 unforced errors and dropping serve twice in the first set.
It was the first time Nadal, who has not dropped a set at the tournament yet, had played in the hot conditions of the Perth day session.
“It’s the first time I played under these heavy conditions, so the feeling on court is completely different,” said Nadal, who will be seeking to equal Roger Federer’s record of 20 Grand Slam singles titles at the Australian Open, which starts on 20 January.
He said he was not thinking about catching the Swiss great, adding: “My only goal is to keep playing good tennis, keep enjoying this sport and being happy. And if that happens and I stay healthy then the goal is to keep producing chances in the events that I’m going to play.”
The ATP Cup is a new 24-nation knockout tournament that has been set up by the men’s professional tour to kick off the 2020 season.
It features six groups of four teams, who each play three round-robin ties in an event played across Sydney, Brisbane and Perth.
Among the other countries who have already qualified for the quarter-finals are Great Britain, who face hosts Australia on Thursday.
Novak Djokovic’s Serbia and Russia are also through to the knockout stage, which will be played in Sydney.