Serena Williams continues her match through the Australian Open in the next day of play at Melbourne. Sister Venus Williams faces her most difficult challenge in the tournament.
And while Novak Djokovic meets an unseeded player, attention in the men's draw will be on a clash between David Ferrer and Kei Nishikori.
Most pretenders have been eliminated, and now the world's best tennis players meet equally qualified opponents as Aussie heads toward championship play.
Matches starts at 7 p.m. ET.
Watch this one on the women's side: 11th seed Dominika Cibulkova stands in the way of resurgent Victoria Azarenka, who shows she once again is capable of title contention.
Serena, No. 1 in the women's draw, goes against Spain's Garbine Muguruza, No. 24. Williams showed vulnerability at times at Melbourne, so this match will be anything but easy.
Venus has a sterner test: Agnieszka Radwanska, seeded sixth. Williams had a strong first week, showing she is capable of playing at levels of her younger years. But Radwanska enters as the favorite.
Two other American women will be in action. The battle of the Madisons will send on to the sidelines, either Madison Keys or Madison Brengle. Keys' strong play under coach Lindsey Davenport is the talk of the tournament. And Brengle is also among top storylines as she returns to prominence after a career low point.
Watch the Ferrer-Nishikori match. Spain's Ferrer will be a stout opponent for Nishikori, Japan's rising star in a clash of top-10 seeds.
Here are the Monday singles matches at Melbourne Park. All times ET.
Rod Laver Arena
Dominika Cibulkova (11), Slovakia, vs. Victoria Azarenka, Belarus
Serena Williams (1), United States, vs. Garbine Muguruza (24), Spain
David Ferrer (9), Spain, vs. Kei Nishikori (5), Japan
Venus Williams (18), United States, vs. Agnieszka Radwanska (6), Poland
Novak Djokovic (1), Serbia, vs. Gilles Muller, Luxembourg
Margaret Court Arena
Stan Wawrinka (4), Switzerland, vs. Guillermo Garcia-Lopez, Spain
Madison Keys, United States, vs. Madison Brengle, United States