Karolina Muchova was unseeded at the US Open, reflecting her ranking of 52nd in the world, but given she reached the semi-finals at Flushing Meadows last year she was clearly more of contender than that status suggested.
So it has proved with the Czech knocking out Italian fifth seed Jasmine Paolini, a finalist at both the French Open and Wimbledon this year, 6-3 6-3 to reach the last eight on Monday.
Muchova was herself a Paris finalist in 2023, but needed surgery on her right wrist in October, sidelining her for 10 months.
"This was my worst and most serious injury. But I love the sport, so in my head, I was, 'I will do everything I could to (get) better and try.' And here I am today," Muchova said.
"I'm just a really happy kid now."
Also through in the same half of the draw is sixth seed Jessica Pegula, who beat Russian 18th seed Diana Shnaider 6-4 6-3.
Asked what she needs to do to get to the semi-finals this time, Pegula joked: "I always say I just need to win the next match to get to the semis, and then that'll solve everything, right?
"It doesn't really matter to me. Every match is every match. I've always played it like that. It just so happens to be quarter-finals, but at the same time, to be able to say I've been in that position many, many times is great. I just have to keep putting myself there and keep trying to play my game."
Pegula has the momentum having won 13 of her past 14 matches, all on hard courts. But in her fourth round tie she'll be up against world No.1 Iga Swiatek, who beat her in two of those quarter-final outings.
The Polish top seed walloped Liudmila Samsonova 6-4 6-1 to keep her pristine sprint on track at Arthur Ashe Stadium.
Swiatek, the only former champion remaining in the women's draw, has not lost a set since she arrived in New York and looked every bit the veteran in her 100th major match as she dropped only four of her first serve points.
When she captured the 2022 US Open for one of her five grand slam titles, she eliminated Pegula in the quarters.
Indeed, half of Pegula's six quarter-final exits at slams came against a No.1 player — Swiatek twice and Australia's Ash Barty once.
"I'll just try to draw from those experiences and kind of how I felt going into the next match, but it's just so tough," Pegula said.
"I mean, I know you don't want the cliche answer, but it's just kind of one match at a time, and every day kind of feels different. It depends on who you are playing, how the conditions are, when you're playing. There are so many variables day to day."
Muchova will next meet Beatriz Haddad Maia, who got past 2018 Australian Open champion Caroline Wozniacki 6-2 3-6 6-3 to become the first Brazilian woman in the US Open quarters since Maria Bueno in 1968.
Haddad Maia, the 20th seed, was a semi-finalist at the French Open last year but had not been past the second round at Flushing Meadows until now.
Wozniacki, the 34-year-old Dane and two-time US Open finalist, has enjoyed her time in New York since coming out of retirement in 2023 but could not better last year's run to the fourth round.
With AP & Reuters.