Jessica Pegula, daughter of Bills, Sabres owners, into quarterfinals at Australian Open

Pegula fired up after upsetting No. 5 Svitolina (0:18)

Jessica Pegula notches the first win against a top-10 opponent in her career as she advances to the quarterfinals in the Australian Open with a win over No. 5 Elina Svitolina. (0:18)

MELBOURNE, Australia -- Jessica Pegula's first victory over a top-10 opponent earned the 26-year-old American her first trip to the quarterfinals of a Grand Slam tournament.

The 61st-ranked Pegula, whose parents own Buffalo's Bills and Sabres franchises, held on to beat No. 5 seed Elina Svitolina of Ukraine 6-4, 3-6, 6-3 in Rod Laver Arena on Monday.

She will face No. 22 Jennifer Brady in an all-American quarterfinal.

After her upset victory, Pegula scribbled on the screen of an Australian Open courtside TV camera: "hi mom, hi dad, see you next rd Jen B.''

In addition to a shoutout to her parents, that was a message for Brady, a good pal of Pegula's whose fourth-round match was to follow hers in Rod Laver Arena.

And after Brady won too, setting up an all-American matchup against Pegula with a berth in the final four at stake, she used a blue marker to respond in kind, writing: "Bring it Jess!''

"It's an opportunity for both of us,'' Pegula said, recalling that she and Brady became close after playing doubles together for the United States in the team competition now known as the Billie Jean King Cup. "I'm just happy I'm here; she's been playing some good tennis, solidifying herself as a top player.''

Pegula is on quite a breakthrough run. She has won four matches at Melbourne Park over the past week -- including victories against two-time Australian Open champion Victoria Azarenka and 2011 US Open champion Samantha Stosur -- after entering the hard-court tournament with a total of three wins at majors for her career.

Also significant for Pegula, who works with Venus Williams' former coach David Witt: She came into the day with an 0-6 record against top-10 women.

Witt said Pegula's rising confidence is a big part of her progress. She found a sort of kinship with her family's football team, the Bills, who made the playoffs three of the past four seasons behind quarterback Josh Allen after going nearly two decades without a trip to the postseason.

"Even last year, when he wasn't playing that well, I was like, 'I like this kid.' I loved his competitive spirit. He was a gamer. He just wanted to win. That's something you love to see,'' she said about Allen. "It's definitely something I think I tried to take into my game a little bit, even watching the team getting that grit, that competitive attitude, having that mindset; in tennis, it's like 90%, sometimes, of the matches. I think it's been really cool to watch them and kind of channel that energy into how I've been doing.''

With the sky blue and the temperature in the low 70s Fahrenheit -- and zero fans in the stands for the third day in a row because of a local COVID-19 lockdown -- Pegula dictated groundstroke exchanges from right along the baseline.

In the early going, she pushed around two-time Grand Slam semifinalist Svitolina -- who eliminated American teenager Coco Gauff in the second round -- and went up by a set and a break at 1-0 in the second.

Up until then, Pegula had not been broken.

But that's where Svitolina, with everything slipping away, made a stand. She suddenly broke Pegula twice in a row, part of a four-game run that put Svitolina ahead 4-1 in the second on the way to forcing a third set.

As if flipping a switch, or remembering what worked so well earlier, Pegula returned to her more aggressive brand of hit-to-the-corners play and led 4-1. She did get broken to 4-3 but broke right back, then served out the most important victory of her career by grabbing the last four points after falling behind love-30.

Brady made it to the round of eight at Melbourne Park for the first time by defeating No. 28 Donna Vekic of Croatia 6-1, 7-5 with the help of nine aces.

Brady went through two weeks of hard quarantine when she got to Australia last month because someone on her flight tested positive for COVID-19 upon arrival. She was not allowed to leave her hotel room at all during that time.

"A lot of people were complaining, and I told myself I wasn't going to complain,'' Brady said. "I mean, there's way worse things going on in the world than me being stuck in a hotel room for 14 days.''

Brady is from Pennsylvania and played college tennis at UCLA. She was a semifinalist at last year's US Open.

Vekic's right knee was heavily taped by a trainer early in the second set, but she kept things close from there, until 5-all. That's when a double fault handed over a break at love to Brady, who then served out the victory.

Brady and Pegula gave the U.S. at least three women's quarterfinalists at Melbourne Park, joining 23-time Grand Slam champion Serena Williams, who advanced a day earlier.

"I mean, it's pretty awesome to see. I hope we can all push through,'' Pegula said. "The last, I don't know, year or so, we've really all pushed each other. Maybe we haven't said it to each other, but I think we all can feel it.''

Elsewhere, Ash Barty made light of the challenge of unseeded American Shelby Rogers with a commanding 6-3, 6-4 victory to reach the quarterfinals for the third year in a row.

The world No. 1 has tried to deflect talk that she might end Australia's 43-year wait for a homegrown champion next Saturday, but she looked every bit the title contender as she swept into the last eight without dropping a set.

Rogers has played quarterfinals at two Grand Slams and made a habit of upsetting highly ranked players, but she was unable to get enough of a handle on Barty's serve to make her high-quality returns a factor.

Barty faltered for the first time with victory in sight, allowing Rogers to take back one of the two breaks of serve she had given up in the second set, but the top seed fixed a quarterfinal date with Czech Karolina Muchova two games later.

Muchova recovered from a shaky start to defeat Belgian Elise Mertens 7-6(5), 7-5 and reach the last eight.

Mertens, seeded 18th at Melbourne Park, had defeated Muchova in straight sets at the end of last year in Ostrava in their only previous meeting and was cruising at 4-0 in the first set.

But No. 25 seed Muchova then found her range at Margaret Court Arena and soon got back on level terms before taking the opener in the tiebreaker.

The 24-year-old picked up the crucial break in the 11th game of the second set and converted her first match point when Mertens found the net on a return.

The Associated Press and Reuters contributed to this report.