Caroline Wozniacki began her bid to win the New Haven Open for a fifth consecutive year with a comfortable victory over Ekaterina Makarova.
The Danish third seed was a 6-3 6-3 winner over her Russian opponent at Yale as she embarked on a bid to achieve the rare feat.
Only three players have previously won a WTA tournament five years in a row, with Wozniacki looking to follow Martina Navratilova - who won five times in a row at Eastbourne, Wimbledon and Chicago - plus Steffi Graf and Chris Evert into the record books.
If Wozniacki wins this week, it would give the 22-year-old former world number one her first title of a difficult season in which she has contested just one final, at her home event in Copenhagen.
Fourth seed Sara Errani, the French Open runner-up, was tested by wild card Bethanie Mattek-Sands but the Italian edged past her American opponent 6-4 7-5.
Slovakian Dominika Cibulkova and Russian Maria Kirilenko were other seeded winners.
Germany's Mona Barthel was a 6-3 7-5 winner against Cibulkova's unseeded compatriot Daniela Hantuchova, who has struggled for form since the early weeks of the season.