WATCH: Stefan Tsitsipas injures father with racket during on-court meltdown
Stefanos Tsitsipas hurt his father in a mid-match meltdown during his clash with Australia's Nick Kyrgios at the ATP Cup.
Greek captain Apostolos Tsitsipas, who coaches the 21-year-old, was caught by Tsitsipas' angry racket swipe as he reacted to losing the opening set on a tie-break in Brisbane.
Tsitsipas Sr reacted with shock and moved to sit further away from his son, with a bruise visible on his arm.
Tsitsipas was given a warning by the umpire as well as a talking-to from his mother, Julia Apostoli.
— JC 🎾. (@Joe__Tennis) January 7, 2020
At his post-match press conference, Tsitsipas said he was planning to speak to his father, saying: "It happened accidentally.
"I didn't mean to do it and straight away forgot about it and moved on from there. It happens. I wasn't aiming to do that. It's just it went out of control, unfortunately."
The world number six then received a point penalty for hitting a ball in anger early in the second set and, although he levelled the match, it was Kyrgios, for once a picture of control down the other end, who eventually prevailed 7-6 (7) 6-7 (3) 7-6 (5).
The Australian fell on his back after a final backhand winner down the line as the home nation, who were already through to the quarter-finals, maintained their perfect record.
In the last eight, Australia will face Great Britain, who had a helping hand from Belgium in winning Group C.
Britain did their bit with a 3-0 victory over Moldova, meaning a 2-1 win for Belgium against previously-unbeaten Bulgaria would see Tim Henman's side progress.
And that is exactly what played out despite an upset win for Dimitar Kuzmanov over Steve Darcis in the opening rubber.
For once, Bulgarian talisman Grigor Dimitrov could not save his country, going down 4-6 6-2 6-2 to David Goffin before losing alongside Alexandar Lazarov in the deciding doubles rubber.
It was Joran Vliegen and Sander Gille who completed the job for Belgium, winning 3-6 6-4 10-7 to keep alive their country's hopes of qualifying for the last eight as one of the two best-placed runners-up.
Canada are in a similar position following a 2-1 victory over Germany.
Jan-Lennard Struff defeated Felix Auger-Aliassime 6-1 6-4 but Alexander Zverev's miserable tournament continued with a 6-2 6-2 loss to Denis Shapovalov and the young Canadians joined forces to win the deciding doubles.
Russia were convincing winners of Group D thanks to a 3-0 victory over Norway while defeat by Italy meant the USA finished the competition with a 0-3 record.