Serena Williams’ last singles title was the 2017 Australian Open when she was eight weeks pregnant.
Serena Williams reached the Auckland Classic semi-finals with a straight-set victory over Germany’s Laura Siegemund.
The 23-time Grand Slam singles champion beat 73rd- ranked Siegemund 6-4 6-3.
Williams, whose last singles title came at the 2017 Australian Open, will play fellow American Amanda Anisimova after she beat Eugenie Bouchard 6-2 3-6 6-4.
Caroline Wozniacki reached the semi-finals with a 6-1 6-4 victory over the 2019 champion, German fourth seed Julia Gorges.
The Dane, who will retire after the Australian Open in Melbourne, will next play unseeded American Jessica Pegula.