Sydney, Jan. 8 -- Zizou Bergs and Elise Mertens registered singles victories on Thursday as Belgium beat Czechia to power into the semifinals of the mixed-teams United Cup in Sydney, setting up a clash against Switzerland.

In the men's singles, Bergs continued his giant-killing run after beating world No. 18 Jakub Mensik 6-2, 7-6 (4) in one hour and 40 minutes.

Bergs, ranked 42, has started the season riding a wave of momentum having stunned world No. 5 Felix Auger-Aliassime in straight sets on Tuesday.

The 26-year-old's confidence was evident when he stormed through the first set against a ragged Mensik.

Bergs' dominance continued in the second set until nerves set in and he struggled to close out the match on serve.

"You just want to...