The Polish, solid number 1 in the world, is looking to revive after a surprise defeat in the final of the Ostrava tournament against the Czech Barbora Krejcikova last week.
For her part, the 18-year-old American, 8th in the WTA rankings, is looking to secure her place for the Masters which will be played in Fort Worth, Texas from October 31 to November 7.
Gauff is notably in the fight with the American Jessica Pegula, who defeated her compatriot Coco Vandeweghe 6-3, 6-1, and who will play against another American, Madison Keys, for a place in the semi-finals.
Another American in the running, Danielle Collins will have a lot to do against the Spaniard Paula Badosa, second seed in San Diego. The 4th in the world was particularly expeditious against the American qualifier Louisa Chirico in less than an hour 6-0, 6-3.
The table is completed by the Croatian Donna Vekic, 77th player in the world after qualifying and surprise winner ahead of the Czech Karolina Pliskova in the second round 6-3, 6-2.
