Greece's Stefanos Tsitsipas was clinical as he picked up his first win of the season at the ATP Cup in Brisbane on Sunday against a temperamental Alexander Zverev of Germany, who was almost reduced to tears due to problems over his serve.
Nick Kyrgios' late withdrawal due to a back problem did not stop Australia from defeating Canada, as the hosts became the first to seal a quarter-final spot with their second 3-0 win in the inaugural team event.
Australia had beaten Germany in their opening tie and qualified for the final eight stage in Sydney as Group F winners after Germany beat Greece 2-1 in the evening session.
ATP Finals champion Tsitsipas made it five straight wins against the German world number seven with a breezy 6-1 6-4 victory as Zverev cut a frustrated figure with 10 double faults and a first serve percentage of just 45%.
Tsitsipas returned to the Pat Rafter Arena for the deciding doubles but went down 3-6 6-3 (17-15) as Greece suffered their second loss in the ATP Cup, which features 24 nations competing in Perth, Brisbane and Sydney over 10 days.
With just two weeks left until the start of the Australian Open, Zverev needs to find a quick cure for his service woes as he also had 14 double faults in a three-set loss to Australia's Alex de Minaur on Friday.
Zverev smashed his racquet repeatedly when playing against De Minaur and against world number six Tsitsipas he flung his racquet away twice and appeared almost to start crying as he hid his face in his palms after a service break in the second set.
Tsitsipas, who defeated Federer and Dominic Thiem to win the ATP Finals in November, lost his opening match against Canadian Denis Shapovalov in the event but maintained Zen-like focus in the face of all the drama across the court on Sunday and closed out the match under 75 minutes.
Earlier, the mercurial Kyrgios pulled out from the opening singles in Brisbane as a precaution because of a bad back, paving the way for hometown favourite John Millman to take down Canada's Felix Auger-Aliassime 6-4 6-2.
De Minaur then rallied from a set and a break down against fellow 20-year-old Denis Shapovalov to triumph in the battle of next generation stars to seal the tie for Australia.
From 4-2 down in the second set, De Minaur won six straight games to lead 2-0 and ultimately won 6-7(6-8) 6-4 6-2 against the Canadian.
Grigor Dimitrov also led Bulgaria to their second win of the event against Moldova, with Russia's Daniil Medvedev an easy 6-3 6-1 winner against big-serving American John Isner.