Pegula powers into Krejcikova last-16 showdown at Australian Open
The in-form Pegula has reached the quarter-finals on her last two visits to Melbourne Park and can make it a hat-trick if she beats the 2021 French Open champion on Sunday.
The American third seed needed just 65 minutes to canter past erratic Ukrainian Kostyuk, who committed 39 unforced errors to the consistent Pegula's nine.
"I thought I didn't give away a lot of free points. I was playing aggressive when I had to, but also playing smart. So that worked really well," said Pegula.
"I wasn't serving great today, but I thought I served smart enough to get myself through some tough games," added Pegula, who was resilient enough to save eight break points as she dropped her serve just once.
Pegula and Kostyuk had only met on one previous occasion, in Cincinnati last year, with the Ukrainian taking the first set before the American outlasted her 6-7 (5/7), 6-1, 6-2 in 2hr 7min.
There was no chance of a repeat on Friday, Pegula ruthlessly racing to a triple break on her way to taking a first set "bagel".
Kostyuk did finally trouble the scorers at the start of the second, but it proved to be the only game she won on her own serve as Pegula cruised to victory.
Pegula was instrumental in leading the United States to their United Cup triumph two weeks ago, where she beat top-ranked Iga Swiatek in straight sets in the semi-final.
She will face a tough prospect next in 20th seed Krejcikova, who - like Pegula - is yet to drop a set.
"I've watched her quite a bit. She's had a great last couple of years," said Pegula of the Czech, who also breezed past a Ukrainian.
Krejcikova beat the 39th-ranked Anhelina Kalinina, 6-2, 6-3 in 1hr 26min on Rod Laver Arena.
"I think with every single match I'm getting better and better," warned Krejcikova.
"My serve was working really well today, I played really good returns and from the baseline. I played also a very solid game. Today was a really, really great match for me."
