Muchova had put Czechia in the box seat after defeating world No.4 Jasmine Paolini 6-2 6-2 in one hour and 43 minutes at Ken Rosewall Arena.
"I was playing like Novak (Djokovic)," Machac said.
"This kind of tennis is the highest peak of what I can play.
"It's an important point. I was surprised at how I played great without many mistakes.
"I know I can play the best tennis against the best.
"It's going to be tough (against the USA). We are a really small country and the USA is a little bit bigger than us, so let's see.
"But I think we have a great chance to be in the final. We will fight. We will do everything."
On another level 🚀— United Cup (@UnitedCupTennis) Machac seals the spot in the semis for Team Czechia with a 6-1 6-2 win over Cobolli 👊#UnitedCup pic.twitter.com/lqJZuud3CPJanuary 3, 2025
Defeat to Czechia marks a disappointing end to Italy's campaign, after they won the past two Davis Cups and were runner-up two years ago to the US in the inaugural edition of this season-opening mixed teams' event.
Adding more salt to the wound, Italy had not lost a rubber in Sydney until Friday.
Paolini had been a formidable force in the tournament in world No.1 Jannik Sinner's absence, only dropping four games in the group stage.
But the 2024 break-out star struggled to fire against Muchova, being broken twice in the opening set before also losing her first service game in the second.
The Czech star then staved off giving away a break point in the final game to storm home.
First set goes to Muchova 💪— United Cup (@UnitedCupTennis) #UnitedCup pic.twitter.com/axxUds4oJQJanuary 3, 2025
Muchova has had the upper hand over Paolini in all five meetings, having knocked the Italian out of the US Open in straight sets twice.
"I know Jasmine is an unbelievable player. It was really a tough match," Muchova said.
"She put every ball back. I just tried to play aggressive. It worked well in the past matches and tonight.
"I really wanted to bring a point to the team so I was trying to stay focused.
"I know I had to go until the end. I'm really happy I made it."
Czechia's top men's player Machac sealed the deal facing little resistance from Cobolli, claiming victory within 54 minutes.
It was an uncharacteristic performance from the Italian, who had opened his season by defeating Switzerland's Dominic Stricker in straight sets before saving a match point to pull off a victory over world No.14 Ugo Humbert.
