Bergs upsets Mensik as Belgium beat Czech Republic to reach United Cup semis

Zizou Bergs stunned world number 18 Jakub Mensik and Elise Mertens outplayed Barbora Krejcikova as Belgium beat the Czech Republic 2-0 in the United Cup quarterfinals on Thursday to set up a last-four clash with Switzerland.

Mensik struggled with double faults in the second set as Bergs won 6-2 7-6(4), before Mertens beat Krejcikova 5-7 6-1 7-5 to seal the tie.

Bergs, ranked 42nd in the world, landed four aces as he took the first set in 31 minutes, and kept his cool through a tense second-set tiebreak to clinch his second straight win over a top-20-ranked opponent, having beaten Canadian world No 5 Felix Auger-Aliassime in the group stage.

"You’re so close, you’re playing big points. I got tight, I go backwards, I play defensive. So it was a very big struggle in the end. I'm so happy for myself and the team," Bergs said.

Mertens wore down two-time Grand Slam winner Krejcikova who committed seven double faults in the third set.

"I felt like I had to play a little aggressive... I'm really happy I could turn it around. It was 1-0 for Belgium, so I could play freely, thanks to Zizou," Mertens said.

Australia face Poland on Friday for a place in Saturday's first semifinal against the United States.