Five-time Wimbledon champion Venus Williams won and top-ranked Angelique Kerber lost.
Williams, who last won the title at the All England Club in 2008, advanced to the Wimbledon quarterfinals by beating 19-year-old Ana Konjuh 6-3, 6-2 yesterday.
Williams is playing at the grass-court major for the 20th time in her career, with her Wimbledon debut coming a few months before Konjuh was born.
Kerber, who reached the Wimbledon final last year but lost to Serena Williams, was beaten by Garbine Muguruza on No. 2 Court, 4-6, 6-4, 6-4.
With the loss by Kerber, either Simona Halep or Karolina Pliskova will take over as the top-ranked player after the tournament.
Williams will next face French Open champion Jelena Ostapenko in the quarterfinals. The 20-year-old Latvian, who won her first tour-level title at Roland Garros last month, beat fourth-seeded Elina Svitolina 6-3, 7-6 (6) on Court 12.
Ostapenko led 5-3 in the second set, but was broken and forced into a tiebreaker. She finally won by converting her eighth match point.
Ostapenko had never before been past the third round at a major tournament prior to this year's French Open. She was the first woman to win her debut tour-level title at a Grand Slam tournament since 1979.
At Wimbledon, the Latvian is into the quarterfinals for the first time. However, the 20-year-old Latvian won the girls' title at the All England Club in 2014.
Two-time Grand Slam champion Svetlana Kuznetsova and Magdalena Rybarikova also advanced to the quarterfinals.
The second Monday at Wimbledon is, arguably, the busiest day in tennis. All 16 fourth-round matches at the All England Club are played on the same day, a schedule that will produce all eight male and all eight female quarterfinalists.
Andy Murray was on Centre Court against Benoit Paire, and Roger Federer will follow.
On No. 1 Court, Johanna Konta was up first, followed by Rafael Nadal. Novak Djokovic is third.
Kuznetsova was the first to finish her match on Monday, beating Agnieszka Radwanska 6-2, 6-4.
The seventh-seeded Russian is a two-time Grand Slam champion who will be playing in the Wimbledon quarterfinals for the fourth time. She has never advanced past that stage.
In the quarterfinals, Kuznetsova will face Muguruza.
Rybarikova, who beat Pliskova in the second round, defeated Petra Martic of Croatia 6-4, 2-6, 6-3 and advanced to the Wimbledon quarterfinals for the first time.
Rybarikova missed nearly seven months after last year's Wimbledon because of injuries.