Greek Tsitsipas serves up win over Zverev

A smouldering Alexander Zverev's serving woes have worsened in an angry straight-sets loss to Stefanos Tsitsipas in the ATP Cup.

Greek world No.6 Tsitsipas beat Germany's world No.7 6-1 6-4 in Brisbane on Sunday night to keep his country afloat in their tie, and the tournament.

Zverev cut an exasperated figure as he traded words with his team between games, before finishing with 10 double faults and a first serve success rate of 45 per cent at Pat Rafter Arena.

It followed 14 double faults in a three-set loss to Australia's Alex de Minaur on Friday night.

Zverev smashed his racquet and steamed after losing from one set and a break up against the Australian.

But he was never in that position in this high-profile clash - the first top-10 meeting in ATP Cup history - with the Greek dominating the first set and coming from an early break down in the second.

The win was Tsitsipas's first in the tournament and ensured their encounter progressed to a decisive doubles tie, after Jan-Lennard Struff thrashed Michail Pervolarakis 6-4 6-1.

The two best-performed second placed teams from the six groups spread across Sydney, Brisbane and Perth will join the six group winners in the quarter-finals in Sydney.

Greece were beaten 3-0 by Canada on Friday while Germany were swept by Australia, meaning the loser of Sunday's clash will drop to 0-2 and effectively out of quarter-finals contention.