Andrea Petkovic shut down a troll after he told her to change her career following a defeat to Petra Kvitova in an exhibition game.
The 15-year-old Coco Gauff reached her first-ever WTA final and became the youngest woman to do so in 15 years.
Andrea Petkovic eased past Italian Camila Giorgi in her opening game at the Dubai Open.
Jiri Vesely defeated Lleyton Hewitt, who will retire after the Australian Open, 6-3, 6-7 (1), 6-4 before Karolina Pliskova came from 3-1 down in the second set to beat Jarmila Wolfe Gajdosova 7-5, 6-3 at Perth, Western Australia.
Footage of the incident quickly did the rounds on social media, with some contributors accusing her of racism. But on Monday, Petkovic insisted she didn't mean to be rude.
Russia's Kuznetsova, the winner of 2009 French Open and 2004 US Open, lost the lop-sided match 0-6, 1-6 to her compatriot Anastasia Pavlyuchenkova.
Germany, the 2014 finalists, will face Russia away in the semi-finals on April 18-19 after Petkovic again dug deep to seal a 6-3, 3-6, 8-6 win over Jarmila Gajdosova, with the third set of their fourth singles rubber taking nearly an hour.
The Czechs are eyeing their third Fed Cup win in four years after lifting the trophy in 2011 and 2012. Germany are looking for their first title since 1992, when a team led by Steffi Graf and current captain Barbara Rittner won the title.
Monica Puig, seeded eighth in the event and ranked 48th in the world, outlasted 92nd-placed Watson 6-4, 6-4 in 94 minutes.
Sania and Huber will now fight it out with Romania's Monica Niculescu and Czech Republic's Klara Zakopalova for a place in the semifinals.