Stephens was seeded fourth in the season's first clay-court event. She pulled out of the tournament Monday.

Stephens said in a statement she was sorry to miss the event, but her championship play in Miami "left me completely exhausted/fatigued both physically and mentally."

Stephens defeated Jelena Ostapenko 7-6 (5), 6-1 to win the Miami tournament.

Stephens, 25, said she did not feel ready to play her best tennis and decided it was in her best interest to get some rest.

The American won her first major, the US Open, last September.

Naomi Osaka of Japan and Daria Gavrilova of Australia were among the seeded players to advance in the opening round of the Volvo Car Open on Monday.

Osaka, seeded No. 10, topped Jennifer Brady of the United States 6-4, 6-4. Gavrilova defeated Ons Jabeur of Tunisia 1-6, 6-4, 6-3.

Other seeds who moved on at the Daniel Island Tennis Center were No. 12 Kiki Bertens of Netherlands, No. 14 Alize Cornet of France and No. 15 Mihaela Buzarnescu of Romania.

Most of the top seeded players, including No. 1 seed Caroline Garcia of France, will begin play on Tuesday.