Caroline Wozniacki's disappointing season continued Monday in New Haven, Conn.
Latvia's Jelena Ostapenko downed Wozniacki, formerly the world's top-ranked player, 7-5, 6-2 in the opening round of the Connecticut Open.
Wozniacki, a 26-year-old Dane, hasn't won more than two singles matches in an event all season, causing her ranking to fall to No. 51. She fell in the first round of the Australian Open, missed the French Open with an ankle injury and lost in the opening round at Wimbledon.
A four-time New Haven champion, Wozniacki lost in the second round of singles play at the Rio Olympics to the Czech Republic's Petra Kvitova, who went on to grab a bronze medal.
Ostapenko, who is ranked 39th, has yet to claim a WTA championship. She dropped her opening-round match in Rio to Australia's Samantha Stosur.
In other first-round action, Russia's Elena Vesnina, a Rio doubles gold medalist, downed Italy's Camila Giorgi 6-1, 6-4.
"The best moment in our lives -- I can say that for sure," Vesnina told the Hartford Courant. "We've been watching Olympics in the past, since we were kids, athletes were standing on the podium with the national anthem playing -- it doesn't matter what country -- we were dreaming just to be there. To stand and get the gold medal for your country -- it's top level. It's over the top level."
Vesnina reached the singles semifinals at Wimbledon this summer, falling to Serena Williams, but she dropped her first-round match in her most recent singles event, at Montreal.
Kvitova, the sixth seed, rebounded to beat qualifier Louisa Chirico of Westchester, N.Y., 1-6, 6-1, 6-3. Kritova was the only seeded player who had a match Monday.
France's Caroline Garcia topped Romania's Irina-Camelia Begu 6-1, 6-4, and Canada's Eugenie Bouchard defeated Germany's Annika Beck 6-2, 6-1.
In a battle of qualifiers, Anastasija Sevastova of Latvia knocked out American Nicole Gibbs 7-5, 6-0.
Two other qualifiers posted first-round wins: Croatia's Ana Konjuh and Latvia's Anastasija Sevastova.