Alexander Zverev and Stefanos Tsitsipas suffered frustration on day five of the ATP Cup, as Russia and Great Britain joined Australia and Serbia in the quarter-finals.

Germany were eliminated after a 2-1 defeat to Canada where a troubled Zverev lost his third consecutive match of the tournament.

He went down 6-2 6-2 to Denis Shapovalov in 70 minutes after also suffering defeats to Alex de Minaur and Tsitsipas in his country's first two ties.

Jan-Lennard Struff had beaten Felix Auger-Aliassime, but the Canadian later teamed up with fellow youngster Shapovalov to win the decisive doubles against Kevin Krawietz and Andreas Mies in straight sets.

Australia had already won Group F, so Canada will wait for the results on day six to see if they will progress as one of the two best runners-up.

"I'm really happy to get the win and hopefully we can go through," said Shapovalov.

"I feel like we're definitely one of the top teams and I feel like we definitely deserve to go to Sydney. Hopefully, if we do get that chance, we can do some really big damage."

Zverev's serving woes continued as he won only 29 per cent of points on his second serve and had seven double faults, taking his weekly total to 31 in three matches.

The world number seven said: "There's a lot of things that I still need to improve, but it's the start of the season."

Hosts Australia kept up the momentum by winning their third straight tie against Greece, as Tsitsipas fell to defeat.

With De Minaur rested, Nick Kyrgios took over number one duties and won a tense encounter 7-6 (9-7) 6-7 (3-7) 7-6 (7-5).

Tsitsipas inadvertently injured his father Apostolos when smashing his racket in the team zone after losing the opening set tie-break and Greece ended the week without winning a tie.

But the ATP Finals champion was in a reflective mood afterwards, saying: "We had a difficult draw here in Brisbane.

"Canada, Australia … Germany, one of the strongest nations in the game, playing against a small, tiny little nation like Greece, which has no history in tennis at all? 

"You've got to feel proud. We fought very hard and we wanted to prove to the rest of the world that we can play tennis anywhere."

Russia booked their place in the quarter-finals with a 3-0 win over Norway, Daniil Medvedev handing Casper Ruud his first singles defeat of the week.

Italy were victorious against the United States but cannot reach the next stage despite winning two of their three Group D ties.

Great Britain won 3-0 against Moldova and Belgium's 2-1 win over Bulgaria meant Tim Henman's team progressed as Group C winners and will face Australia in Sydney on Thursday.

Belgium, like Canada, face a nervous wait for Wednesday's results with Spain, Croatia, Japan, Austria, South Africa, France and Argentina the other countries vying to fill the four remaining spots.