But Riske simply played so cleanly, delivering twice as many winners as unforced errors, 30-15, and won her fourth consecutive three-setter in the tournament.
Roger Federer glided into the Wimbledon quarterfinals as he outclassed Italian youngster Matteo Berrettini, with the Swiss legend joining fellow tennis big guns Rafael Nadal and Novak Djokovic in the last eight.
"I am not comparing myself with a year ago, that was the best because I won the French Open". "She's one of my role models, so it was just cool to see that she knows I exist". The Spanish player said: "I just will tell her that enjoy, and just work hard off court every time that she's on-court or in the gym".
Atlanta-born Gauff, who nickname is Coco, certainly doesn't appear short of confidence, stating repeatedly in the opening week of Wimbledon that she is in the competition to win it.
"I don't know my schedule right now because I wasn't expecting to be here, but my next goal would be to win the next tournament I play".
"I saw the last couple of games when she qualified..."
"There aren't many holes in her game, full-stop", said Barty, who followed up her first Grand Slam championship at Roland Garros last month, then grabbed a title at a grass-court tuneup tournament. "I had to take it to Ash".
Alison Riske, a 29-year-old Pittsburgh native, came back from a loss in the first set to knock out No. 1 ranked Ashleigh Barty, 3-6, 6-2, 6-3, on Monday.
As she stepped out onto Court 1, her father Corey Gauff gave her a kiss on the cheek for good luck.
But first up for the defending champion and 16-time major victor is 21-year-old Ugo Humbert from France who is playing in his first Wimbledon.
But Riske took her chances when she got them, breaking Barty four times on four attempts, including to take a 5-3 lead in the deciding set before serving it out.
"I still want to go to college".
Halep, who had given an indication of her form when dismissing the risky Belarusian Victoria Azarenka in the last round, had to work hard before eventually taking a relatively even first set.
Williams won six straight games from 3-2 in the first set to take control of the match.
Also, No. 19 Johanna Konta eliminated two-time champion Petra Kvitova 4-6, 6-2, 6-4, No. 8 Elina Svitolina beat No. 24 Petra Martic 6-4, 6-2, Zhang Shuai defeated Dayana Yastremska 6-4, 1-6, 6-2, Karolina Muchova beat No. 3 Karolina Pliskova 4-6, 7-5, 13-11, and Barbora Strycova came from a set and break down to beat Elise Mertens 4-6, 7-5, 6-2. And while she broke back to be 1-2 down Halep soon broke again and was in control.
Monday's other ties see 2017 semi-finalist Sam Querrey face last-16 debutant and U.S. compatriot Tennys Sandgren.