Roger Federer saluted Iga Swiatek's miracle shot at the United Cup, declaring 'that was crazy' in response to a tweet from the world number one.

Swiatek - the winner of eight WTA titles in 2022 including the French Open and US Open - helped Poland to a commanding 4-1 victory over Kazakhstan in their opening match in Brisbane.

With the Poles' first win in the competition secure, the 21-year-old helped Hubert Hurkacz put the icing on the cake with a 6-3 6-4 success in their mixed doubles clash against Zhibek Kulambayeva and Grigoriy Lomakin.

Swiatek's moment of brilliance came at 30-15 in game six. Desperately chasing Lomakin's drop volley after a fiercely contested rally, she produced a wonderful backhand slice around the net post to the amazement of everyone inside the Pat Rafter Arena.

The shot was executed on several occasions by 20-time grand slam champion Federer, who retired last year, including in his third-round clash with Nick Kyrgios at the 2018 US Open.

Swiatek subsequently asked the Swiss in a light-hearted tweet: "Do you approve?" - to which he replied: "That was crazy."

The world number one is back in action on Monday when Poland ironically face Switzerland, who boast the likes of Olympic gold medallist Belinda Bencic and three-time grand slam winner Stan Wawrinka in Group B.