Gauff shocked in United Cup, comeback kid Hurkacz stuns Zverev
Gauff had won all six of her previous United Cup singles matches for the USA and had a 3-0 record in mixed doubles.
It was the first win over a top-five player for Bouzas Maneiro.
"I know Coco and she's a fighter," the 42nd-ranked Bouzas Maneiro said in Perth.
"She's there all the time in the match, so I knew that I had to be there, and even if I’m 4-1 up, I have to be there.
"And that was my mentality in the third set. To be with power every point because even if you are 3-0 or 4-0, you have to be ready."
In Sydney, Germany's world number three Alexander Zverev was also on the end of a shock United Cup result, beaten 6-3, 6-4 by Poland's Hubert Hurkacz, who had not played since June because of knee surgery.
"It's been a while since I've been competing. Seven months I've been going through difficult times with the team and it was very challenging," Hurkacz said.
"We went through a long period of time not competing and not knowing when we would be able to be back on court again.
"I was just trying to cherish and enjoy every moment here on the court today."
Former world number six Hurkacz has tumbled to 83rd in the rankings but faced just one break point in his 83-minute victory.
"I was serving quite well. I was finding nice spots, so that's definitely a nice feeling to really have good rhythm on the serve," Hurkacz said.
"Just so pleased with the performance and just also so much fun to see the fans again."
Iga Swiatek will try to close out the tie for Poland against Eva Lys.
The Australian Open starts on January 18.