Two-time defending champion Petra Kvitova survived a scare as she advanced to the second round of the Connecticut Open.
Czech sixth seed Kvitova dropped the opening set but rallied to ease past Louisa Chirico in three at the WTA Premier tournament in New Haven on Monday.
Four-time champion Caroline Wozniacki was not so fortunate, upstaged by Jelena Ostapenko in straight sets.
The likes of Eugenie Bouchard and Caroline Garcia also made it through their first-round matches.
KVITOVA COMPLETES COMEBACK
The 2016 Olympic Games bronze medallist would have wanted an easier start to her campaign in New Haven after she prevailed 1-6 6-1 6-3.
An upset was on the cards when American qualifier Chirico powered through the opening set, converting all three break-point opportunities, while winning 80 per cent of her first serves, compared to Kvitova's 46.
But Kvitova quickly found her way at the start of the second set as she eventually downed the 20-year-old.
WOZNIACKI FALLS AT FIRST HURDLE
It was a day to forget for former world number one Wozniacki.
Winner of four consecutive titles in New Haven from 2008 to 2011 - a haul only matched by Venus Williams in 1999-2002 - Wozniacki suffered a shock 7-5 6-2 defeat to Latvian teenager Ostapenko.
Wozniacki struggled throughout, tallying seven double faults, winning just 44 per cent of her first serves, while she was broken seven times in two sets.
QUICK DAY AT THE OFFICE FOR GARCIA AS VESNINA PROGRESSES
After rain halted Garcia's first-round match at 6-1 5-4 against Irina-Camelia Begu, the Frenchwoman returned to complete the clash.
With Garcia just one game away from advancing to the second round, she successfully served out the match 6-1 6-4.
Elena Vesnina - winner of gold in the women's doubles at Rio 2016 - defeated Camila Giorgi 6-1 6-4.
Anett Kontaveit awaits after the Estonian beat Kiki Bertens 6-3 6-4.
Elsewhere, Nicole Gibbs lost 7-5 6-0 to Anastasija Sevastova, Evgeniya Rodina overcame Maria Sakkari 6-1 5-7 6-2 and Ana Konjuh trumped Kayla Day 6-0 6-3.
BOUCHARD PLEASED WITH HER GAME, WOZNIACKI LAMENTS RHYTHM
After winning through to the second round, the inconsistent Bouchard said: "I feel like when I'm on and playing well, my game is right up there with the top players in the world. But at the same time, I want to have that consistency where the bottom end of that is not so low where I've had bad losses like I had this year."
The day's biggest casualty, Wozniacki, added: "It wasn't my best match, but you have to go with it and give her credit where credit is due. Not having played much and it doesn't help when you are trying to find your rhythm out there, I usually grind really well and it was really tough, then she played some good shots."
TOP SEED TAKES CENTRE STAGE
The tournament's number one seed Agnieszka Radwanska gets her campaign underway against Ostapenko in the second round on Tuesday. Belinda Bencic faces Lesia Tsurenko and Ekaterina Makarova meets Sevastova in the other notable clashes.