Katie Boulter booked Great Britain's spot in the quarter-finals of the United Cup with victory over Australia's Olivia Gadecki.

After their win over Argentina in the team competition on Monday, Britain knew one straight-sets success from three rubbers would be enough to see them top the group.

Boulter duly delivered with a dominant 6-2 6-1 victory against 97th-ranked Gadecki in Sydney.

The tie pitted the newly-engaged Boulter against fiance Alex De Minaur, who is Australia's number one player, and she said in her on-court interview: 'I'm very happy to start my new year like that.

'I feel like I've actually lost a lot of sleep recently over the thought of playing my fiance in doubles so I'm so tired and just very happy to get through this rubber.'

De Minaur later beat Billy Harris in the men's singles in straight sets.

However, although Boulter will take part in the mixed doubles, De Minaur won't, meaning the couple won't play against each other.

Boulter will instead play with Charles Broom against Ellen Perez and Matthew Ebden, yet the result won't have an impact on GB's progression, where they will take on Italy in the quarter-finals. 

Earlier, Kazakhstan became the first team to reach the semi-finals thanks to a 2-1 victory over Germany.

World number two Alexander Zverev could be a doubt for the Australian Open after pulling out of the tie with an arm injury.

He was replaced by Daniel Masur, who lost out 6-7 (5) 6-2 6-2 to Alexander Shevchenko after Elena Rybakina had comfortably beaten Laura Siegemund, with Germany winning a consolation doubles.

Iga Swiatek has made a strong start to the year and she again won two matches for Poland in their 2-1 victory over the Czech Republic.

The world number two beat Karolina Muchova 6-3 6-4 and then teamed up with Hubert Hurkacz for a 7-6 (3) 6-3 win in mixed doubles against Muchova and Tomas Machac, who had earlier beaten Hurkacz in singles.