Kvitova held her opening service game to love, captured 14 of the first 15 points, and the first five games.
Petra Kvitova secured the best win of her comeback so far, beating Kristina Mladenovic to reach the semi-finals of the Aegon Classic in Birmingham.
Kvitova, a two-time Wimbledon victor, was viciously attacked by a knife-wielding man on December 20 in her Czech Republic home.
She lost the first set to Muguruza, who reached the Wimbledon final in 2015, but started to showcase her touch and power in the second set, with one incredible victor drawing gasps from the crowd.
"I'm enjoying playing again", said the former world number two. "I like big matches, and I've missed it over the last six months".
"It wasn't my choice to have a break but I always try to see positive things".
Barty overcame Spain's Garbine Muguruza 3-6 6-4 6-3 in the other semi-final in Birmingham.
The tournament's other Grand Slam victor, former French Open champion Garbine Muguruza, also reached the semifinals, only her third of the year and the first on grass since she reached the final of Wimbledon almost two years ago. "I just believed that I could pull it out and win it", she added.
"The hand is good, which is the best news I could have", she said. It's all about consistency with Muguruza, as we know what she's capable of when playing at a high level, but the significant drops in play make her very tough to back. With the momentum on her side, Ashleigh opened up a 5-1 lead in the final set with breaks in games 3 and 5, moving just a game away from the triumph.
"I think that we have really similar games", Kvitova said about her dominance over her fellow Czech lefty.
Kvitova had 16 winners to just eight unforced errors and won 80 percent of points behind her first serve, striking five aces, and moved to a 10-0 career record against Safarova.
Muguruza, a former Wimbledon finalist, could not contain Barty's comeback.
Barty and Muguruza will clash in a contrast of styles for the right to face Daria Gavrilova's quarter-final conqueror Lucie Safarova or dual Wimbledon champion Petra Kvitova in the final. "I like slicing it around on the grass, and I didn't do much wrong".
Barty won the Wimbledon girls title six years ago and proved a revelation in the way she used slice to blunt her famous opponent's attack before counter-attacking with heavy forehand drives.