The Italians finished a superb 2024 season by sweeping the men's Davis Cup and the women's Billie Jean King Cup titles but ran out of steam in the $10 million mixed team event ahead of this month's Australian Open.
Tomas Machac produced a dominant display for a 6-1, 6-2 win over Flavio Cobolli in 54 minutes, sending the Czechs into their first semi-final in the tournament following group stage exits in their previous two attempts.
"I think this kind of tennis is the highest (level) that I can play," Machac said.
"I'm really happy I was able to play this kind of a match today, especially since it's an important point. I was surprised that I was able to play great without any mistakes. I didn't give him any opportunity to come back. That was the key.
"I was trying to be as strong as possible mentally on the court and I was playing like Novak (Djokovic)."
Karolina Muchova put on another masterclass with her inventive brand of tennis in the opening match at Ken Rosewall Arena and sealed a 6-2, 6-2 win over French Open and Wimbledon runner-up Jasmine Paolini.
"I really wanted to bring a point to the team, so I was trying to stay focused," United Cup debutant Muchova said after extending her record over the world number four to 5-0.
"Jasmine is an unbelievable player. It was a really tough match and I knew I had to go until the end. She had many break point chances. I served well. I'm really happy I made it."
Kazakhstan take on Poland in the other semi-final that takes place on Saturday. The final will be held a day later.