Kyrgios beat Jan-Lennard Struff 6-4 7-6 (7-4) in Brisbane, sending down 20 aces after his pledge to give $200 to the bushfires effort for each service winner he hits in January.

Alex de Minaur, Kyrgios's team-mate at the event, who impressively came from a set down to defeat an ill-tempered Alex Zverev 4-6 7-6 (7-3) 6-2, followed suit after Kyrgios tweeted his intention to help, while stars from other sports have also joined in.

"I don't really care about the praise too much. I just think we've got the ability and platform to do something like that," Kyrgios said when asked about the movement he inadvertently started.

"My home town is Canberra and we've got the most toxic air in the world at the moment, so it is pretty sad. It's tough."

Having appeared choked up at that point, Kyrgios added: "I just chucked up a tweet and everyone got behind it. It is bigger than tennis.

"It's going to all the families, firefighters, animals, everyone who is losing homes, losing families. It's a real thing.

Australia completed a 3-0 Group F win after Chris Guccione and John Peers beat German doubles pair Kevin Krawietz and Andreas Mies 6-3 6-4.

In the section's other match, Canada was similarly dominant against Greece, with Denis Shapovalov winning a pair of tie-breaks to best Stefanos Tsitsipas after Felix Auger-Aliassime demolished Michail Pervolarakis 6-1 6-3.

Auger-Aliassime and Shapovalov then combined to win the doubles rubber against the same opponent, prevailing 6-2 6-3.

Great Britain and United States both allowed leads to slip against Bulgaria and Norway respectively.

In Group C, Cameron Norrie beat world number 423 Dimitar Kuzmanov in three sets and Dan Evans made a fast start against Grigor Dimitrov to go a set up.

But Dimitrov prevailed 2-6 6-4 6-1 and he and Alexandar Lazarov triumphed after three tie-breaks against Jamie Murray and Joe Salisbury in the small hours of the Sydney morning.

Taylor Fritz beat Viktor Durasovic 6-2 6-2 and John Isner had United States in charge of the second singles rubber when he took the opening tie break versus Casper Ruud, only for two match points and a second breaker to go against him. He eventually lost, going down 7-5 in the deciding set.

Ruud and Durasovic then recovered from dropping the first set to beat Austin Krajicek and Rajeev Ram 10-5 in a match tie-break in Perth.

Steve Darcis and David Goffin inspired Belgium to a 3-0 Group C win over Moldova, while Daniil Medvedev's 1-6 6-1-6-3 victory against Fabio Fognini helped clinch a 3-0 victory for Russia against Italy in Group D.