Legendary sisters Serena and Venus Williams face each other in the 31st instalment of a rivalry going back 22 years, marking the third decade in which they have squared off. Serena leads the overall head-to-head 18-12, including 11-9 on outdoor hard courts, 7-5 on US soil and nine of their last 11 contests dating back to Miami 2009.
Serena and Venus's first Tour-level match came at the 1998 Australian Open, Serena's Grand Slam debut. Both sisters were unseeded; 16-year-old World No.53 Serena had upset No.6 seed Irina Spirlea in the first round, but fell to 17-year-old World No.16 and eventual quarterfinalist Venus 7-6(4), 6-1 in the second. Their most recent match was in the third round of the 2018 US Open, which Serena - ranked World No.26 in the year of her comeback from maternity leave - took 6-1, 6-2 over Venus, who was again ranked World No.16, en route to her 31st Grand Slam final.
Today's clash will be the Williams sisters' first ever contest at International level. Of their 30 previous matches, 16 occurred on the Grand Slam stage, three at the WTA Finals, eight at Tier I, Premier Mandatory or Premier 5 level, two at Tier II or Premier level (Bangalore 2008 and Charleston 2013) and one at the former Grand Slam Cup exhibition in Munich. Today will also be the earliest Serena and Venus have met in a draw since their first meeting in the second round of the 1998 Australian Open.
40-year-old Venus and 38-year-old Serena's combined age is 79 years and 19 days - the third-highest combined age at a Tour-level match, following 46-year-old Renée Richards' 6-2, 6-2 defeat of 34-year-old Marie Pinterova in the first round of Indianapolis 1981 (combined age 81 years and 348 days), and 31-year-old Amy Frazier's 6-4, 6-4 win over 47-year-old Martina Navratilova in the first round of Charleston 2004 (combined age 79 years and 28 days).
Gallery: Prime rivalry: Serena and Venus prepare for No.31
17-year-old qualifier Leylah Fernandez will bid for her third WTA quarterfinal of the season, and also of her career, in her first meeting with Shelby Rogers. The Canadian teenager has been surging in 2020, with a 15-5 record so far; prior to the COVID-19 pause, she had reached her maiden final in Acapulco as well as notching wins over Belinda Bencic, and Sloane Stephens - the latter of whom she defeated again in the first round this week.
Auckland finalist Jessica Pegula faces a rematch of her first-round all-American derby at that tournament in January against Catherine Bellis, which she took 6-0, 6-4. Former World No.35 Bellis, who reached the Top 50 as an 18-year-old in 2017 but was sidelined for 19 months between March 2018 and November 2019 as she underwent four wrst and arm surgeries, is bidding to reach her first WTA quarterfinal since Doha 2018.
ORDER OF PLAY (all courts start 11am)
Jil TEICHMANN (SUI) vs  Yulia PUTINTSEVA (KAZ)
Not before 12.30pm
 Serena WILLIAMS (USA) vs Venus WILLIAMS (USA)
Not before 2pm
Catherine BELLIS (USA) vs Jessica PEGULA (USA)
[WC] Shelby ROGERS (USA) vs [Q] Leylah FERNANDEZ (CAN)
[WC] Bethanie MATTEK-SANDS (USA) / Sloane STEPHENS (USA) vs  Hayley CARTER (USA) / Luisa STEFANI (BRA)
 Alexa GUARACHI (CHI) / Desirae KRAWCZYK (USA) vs Jamie LOEB (USA) / Ingrid NEEL (USA)
Marie BOUZKOVA (CZE) / Jil TEICHMANN (SUI) vs Kaitlyn CHRISTIAN (USA) / Giuliana OLMOS (MEX)
Not before 3pm
Anna BLINKOVA (RUS) / Vera ZVONAREVA (RUS) vs Magda LINETTE (POL) / Jessica PEGULA (USA)