No.1 seed Sloane Stephens and Pauline Parmentier face off in the first round of Acapulco for the second year in a row. Stephens won last year's tilt 6-4, 6-0, and leads the overall head-to-head 3-1, including 2-0 on hard courts; the Frenchwoman's sole victory was a 6-3, 1-6, 6-4 win in the second round of Strasbourg in 2016.
No.2 seed Danielle Collins and wildcard Victoria Azarenka have only clashed once before - a tightly contested match unfortunately cut short when Azarenka was forced to retire with a back injury while leading 7-6(4), 0-3 in last year's San Jose quarterfinals.
Laura Siegemund leads No.8 seed Johanna Konta 2-1 - but the Briton won the most recent of those matches, also their only hard court encounter, 6-2, 7-5 in the first round of New Haven last year. Siegemund's pair of victories were both on clay - 6-0, 6-2 in the semifinals of the Pelham ITF W25 event in 2015 and 3-6, 7-5, 6-4 in the first round of Madrid in 2017. The pair are also doubles partners this week.
Wildcard Jil Teichmann won her only previous encounter with Bianca Andreescu - a 3-6, 6-4, 7-6(4) epic in the second round of last year's ITF W25 in La Bisbal d'Empordà, Spain on clay. Andreescu has opened 2019 with an 18-2 record so far, including a giant-killing run to the Auckland final and a title at the Newport Beach 125K.
Either No.4 seed Mihaela Buzarnescu or Daria Gavrilova will win their first match of 2019 today. Buzarnescu is on an 11-match losing streak dating back to her unfortunate ankle injury in Montréal last August, while Gavrilova has lost all five of her matches this season so far.
Last year's runner-up Stefanie Voegele is yet to drop a set to Tatjana Maria in three previous meetings - including a 6-2, 7-5 win in the first round here last year, their only match to take place on outdoor hard courts.
Rebecca Peterson reached her maiden WTA semifinal in Acapulco last year, and is also 1-0 against No.5 seed Sofia Kenin, having come from a set and a break down to defeat the American 5-7, 7-5, 6-3 in New Haven qualifying last year.
Wildcard Renata Zarazua captured her first WTA main draw win here a year ago over Kristyna Pliskova, and faces No.7 seed Zheng Saisai today.
ORDER OF PLAY (all courts start 4pm)
Sloane STEPHENS (USA)  vs Pauline PARMENTIER (FRA)
GRAND STAND CALIENTE
After 2 ATP matches
[WC] Victoria AZARENKA (BLR) vs Danielle COLLINS (USA) 
Daria GAVRILOVA (AUS) vs Mihaela BUZARNESCU (ROU) 
Laura SIEGEMUND (GER) vs Johanna KONTA (GBR) 
ZHENG Saisai (CHN)  vs [WC] Renata ZARAZUA (MEX)
Amanda ANISIMOVA (USA) vs [Q] Varvara FLINK (RUS)
Tatjana MARIA (GER) vs Stefanie VOEGELE (SUI)
Timea BABOS (HUN) vs Dalila JAKUPOVIC (SLO)
[WC] Jil TEICHMANN (SUI) vs Bianca ANDREESCU (CAN)
Sofia KENIN (USA)  vs Rebecca PETERSON (SWE)
After 3 ATP matches
Sharon FICHMAN (CAN) / Maria SANCHEZ (USA) vs [WC] Victoria RODRIGUEZ (MEX) / Ana Sofia SÁNCHEZ (MEX)
After 1 ATP match
[Q] Ysaline BONAVENTURE (BEL) vs [Q] Christina MCHALE (USA)