Emma Raducanu had to fend off jet lag as she overcame Elise Mertens in the first round at the Washington Open.

Making her first appearance since she lost in the last 16 at Wimbledon, Raducanu prevailed 6-2 3-6 6-4 over Mertens, who she also defeated at the All England Club, on Monday.

The 21-year-old elected to skip the Olympics to focus on her hard-court form and prepare for the US Open, which she won in 2021.

Raducanu's Washington campaign started with a stern test against Mertens, with the match dragging on well beyond 11pm local time.

And Raducanu conceded it was a struggle as she grappled with jet lag.

"I was playing some pretty good tennis in patches throughout, especially in the first set and moments in the third set," she said.

"I lost some focus in the second. It's not easy playing at 11:30. I got here Thursday night so I'm still jet-lagged.

"I was telling myself, 'I'm not leaving. This is not happening. You're not losing this match'.

"I've been training and playing so good in practice. I've been really on it. So on the court, I was telling myself: 'You've been so focused for so long. There's no way you're not going to try right now. You're going to fight until the very end. You didn't put all that work in for nothing'."

"I'm happy with how I pulled myself out of it, but I do need to focus."

Elena Rybakina is through to the second week at the French Open, following another straight-sets victory over Elise Mertens.

The fourth seed wrapped up a 6-4 6-2 win in 67 minutes on Court Philippe-Chatrier, to book a last-16 clash with either Elina Svitolina or Ana Bogdan.

Rybakina was forced to withdraw injured on the eve of her third-round showdown with Sara Sorribes Tormo at Roland-Garros 12 months ago.

A tight opening set ensued with four successive games from 2-2 going against the serve, but a crucial break to love in the 10th saw the former Wimbledon champion draw first blood. 

She then broke to 15 in game four of the second set to take control of the match, before another in the eighth saw her into the fourth round in Paris for a second time.

Rybakina is joined in the last 16 by home favourite Varvara Gracheva, who continued her groundbreaking run with a straight-sets win over Irina-Camelia Begu.

The Moscow-born 23-year-old, who obtained French nationality last June, is into round four for the first time at a major.

Extending her stay into the second week, having stunned sixth seed Maria Sakkari in the opening round, Gracheva was serenaded with Les Marseillais by the crowd following her victory on Court Suzanne-Lenglen. 

Data Debrief: Rybakina matches Swiatek and Jabeur

Rybakina becomes only the third player to reach the fourth round at multiple majors on clay and grass since the start of the 2020 season.

The 2022 Wimbledon champion joins an exclusive group of players to achieve the feat, along with Iga Swiatek and Ons Jabeur.

Petra Kvitova was one of a handful of seeded players to take the court at the Western and Southern Open on Monday and came away victorious against a past champion of the event. 

The 11th-seeded Kvitova defeated 2019 Western and Southern winner Madison Keys 7-5 6-4 on a rain-plagued opening day of main-draw play at the tournament outside Cincinnati, Ohio. 

The Czech saved eight of nine break points against her serve while breaking Keys three times, and that was enough to pull out the victory. 

Kvitova's countrywoman Barbora Krejcikova, the ninth seed, made her singles debut at the WTA 1000 event with a 6-3 6-2 rout of Daria Kasatkina. 

Fifteenth seed Elise Mertens also was a straight-sets winner, taking down Nadia Podoroska 6-3 6-4, while 13th seed Jennifer Brady defeated Ekaterina Alexandrova 6-3 7-6 (7-3) in a match that finished shortly before 1 a.m. local time.

Though only Krejcikova was in action Monday, the field in Cincinnati includes nine of the top 10 players in the rankings, led by Ashleigh Barty and Naomi Osaka in their first appearances since the Tokyo Olympics. 

In other matches on the first day of play, Heather Watson defeated Aliaksandra Sasnovich 6-2 3-6 6-1, while Paula Badosa outlasted Petra Martic 4-6 6-4 7-6 (11-9) in a two-hour, 34-minute marathon. 

Yulia Putintseva breezed past Zhang Shuai 6-2 6-0, Jelena Ostapenko beat Tamara Zidansek 7-5 6-1 and Jil Teichmann downed Sorana Cirstea 6-2 6-0. 

Angelique Kerber beat Maria Sakkari 6-2 6-2, with Alison Riske matching that scoreline in a defeat of Leylah Fernandez.

Shelby Rogers won 6-4 2-1 when her countrywoman Danielle Collins retired with an injury. 

Crowd favourite Bianca Andreescu was made to work as she opened her defence of the National Bank Open title she won two years ago but the Canadian eventually prevailed in Montreal. 

Andreescu defeated Harriet Dart 6-1 3-6 6-3 in just over two hours in her first match since falling to Alize Cornet in the opening around at Wimbledon. 

That was the latest in a disappointing string of results for Andreescu, who also departed Roland Garros after one match, but the world number eight got back on track Tuesday. 

"Playing at home is so, so awesome," Andreescu said in her on-court interview. "You guys [the fans] show me so much love, especially tonight. I've never had this kind of support before, so I'm so, so grateful."

While Andreescu was able to navigate a challenging opener, three other seeded players were not as fortunate. 

Katerina Siniakova downed fifth seed Garbine Muguruza 6-2 0-6 6-3, while Camila Giorgi ousted ninth seed Elise Mertens 6-3 7-5 and Liudmila Samsonova defeated 12th seed Elena Rybakina 6-4 5-7 6-4.

Having a better time of it were seventh-seeded Petra Kvitova, the 2012 tournament champion, and number 10 seed Anastasia Pavlyuchenkova, who won by identical 6-4 6-4 scorelines against Frenchwomen Fiona Ferro and Carolina Garcia, respectively. 

Eighth-seeded Victoria Azarenka waited out a rain delay to cruise past 2013 finalist Sorana Cirstea 6-2 6-2 in the final match of the day. 

In other action, 15th seed Coco Gauff handled Anastasija Sevastova 6-1 6-4 while her countrywoman Danielle Collins continued rolling after her title in San Jose last week, rallying past Jil Teichmann 4-6 6-1 6-3 for her 11th consecutive match win. 

Two more Americans, Sloane Stephens and Jessica Pegula, prevailed in three sets as well. 

Johanna Konta returned to the court after missing Wimbledon and the Tokyo Olympics due to coronavirus-related issues and advanced when Zhang Shuai was forced to retire up 6-4 2-5 with a leg injury. 

Top seed Elise Mertens was knocked out as Daria Kasatkina won through to the Silicon Valley Classic final where she will meet Danielle Collins.

Fourth seed Kasatkina swept aside world number 17 Mertens in one hour and 21 minutes, winning 6-3 6-2 in San Jose.

The 24-year-old Russian progresses to her fourth final of the WTA season, claiming her third win from four meetings against the Belgian.

The win was former top 10 player Kasatkina's fourth triumph over a top 20 player this year.

Kasatkina broke Mertens three times throughout the match, never dropping her own serve, sending down 4-2 aces.

Mertens was not helped by seven double faults throughout the match, with Kasatkina saving the Belgian's only break point.

Kasatkina will face American seventh seed Danielle Collins who was too good for Ana Konjuh. Collins only needed 52 minutes to win 6-0 6-2 over the Croatian qualifier.

Konjuh struggled on serve throughout, with Collins breaking her six times, while she only won one from 17 points on her second serve.