23:54 CET - Wrapping up the day's tennis, Jiri Lehecka (23) has retired from his second-round match in Rotterdam against Hubert Hurkacz (27) while a set down, meaning the Pole progresses to the quarters.
Over in Dallas, Americans Reilly Opelka (27) and Michael Mmoh (27) have both won their first-round matches to advance.
You can follow the rest of the day's matches from Dallas here - top seed Taylor Fritz (27) will be in action past midnight.
22:36 CET - It's been a day of upsets and we've had another... Second seed Daniil Medvedev (28) has been stunned in Rotterdam by Mattia Bellucci (23). The Italian outsider won their second-round clash 6-3, 6-7, 6-3 to send the Russian home.
22:20 CET - A piece of news that shook the tennis world late yesterday was Romania's Simona Halep (33) announcing her retirement after losing in Cluj.
In memory of Halep's stellar career, we picked out five of the most remarkable moments on her tennis journey.
22:14 CET - Moving back to Dallas, sixth seed Tomas Machac (24) is successfully through to the second round after comfortably beating Kei Nishikori (35) 6-2, 6-2.
21:35 CET - In the last match of the day in Cluj, Viktoriya Tomova (29) has upset second seed Olga Danilovic (24) 7-5, 7-5 to move into the quarter-finals.
The second round continues tomorrow in Romania - check out the full schedule here.
20:55 CET - The day’s play has started in Dallas with Yoshihito Nishioka (29) defeating Bradon Nakashima (23) 6-4, 7-6 to advance to the second round. Jaume Lunar (27) is also through.
18:30 CET - A high-quality clash in Rotterdam has been won by Dutch number one Tallon Griekspoor (28), who has beaten Matteo Berrettini (28) 6-3, 6-7, 7-6 in just under two and a half hours.
17:51 CET - Now the sixth seed is out in Abu Dhabi! In the final match of the day, Anastasia Pavlyuchenkova (33) has been forced to retire while leading Magda Linette (32) 7-5, 1-4.
17:10 CET - Second seed Paula Badosa (27) is the latest big name to be dumped out of Abu Dhabi! The Spaniard lost 6-4, 6-1 to Czech up-and-comer Linda Noskova (20).
Along with Badosa, third seed Daria Kasatkina (27) and fourth seed Yulia Putinsteva (30) have both been bundled out today.
15:57 CET - Another seed has fallen in Abu Dhabi with Daria Kasatkina (27), the third highest-ranked player in the tournament, being beaten 1-6, 7-5, 6-4 by young American talent Ashlyn Krueger (20).
15:24 CET - Fresh off winning in Montpellier, Felix Auger-Aliassime (24) is out of Rotterdam after retiring hurt from his first-round clash with Andrea Vavassori (29) with the match tied at a set apiece.
Over in Abu Dhabi, Ons Jabeur (30) has eased past Wakana Sonobe (17) 6-3, 6-3 to book her spot in the quarter-finals. Next up for Jabeaur is top seed Elena Rybanika (25).
Elsewhere, fourth seed Anhelina Kalinina (27) downed Suzan Lamens (25) 1-6, 6-4, 6-4 to advance in Cluj.
13:55 CET - Top seed Elena Rybanika (25) has won her opening match in Abu Dhabi, beating Katie Volynets 2-6, 6-,4, 6-4 to progress to the quarter-finals. Earlier, Leylah Fernandez (22) also advanced.
Over in Rotterdam, the action is underway for the day with both Arthur Fils (20) and Daniel Altmaier (26) winning their respective first-round clashes.
Lastly, to Cluj, where fifth seed Katerina Siniakova (28) is into the second round after beating Francesca Jones (24) 6-4, 6-7, 6-4.
11:30 CET - The fourth seed in Abu Dhabi is out with Yulia Putinsteva (30) losing 6-2, 6-3 to former Wimbledon champion Marketa Vondrousova (25).
09:48 CET - The first match in Abu Dhabi has been won in dominant fashion by Belinda Bencic (27), who has beaten Veronika Kudermetova (27) 6-0, 6-0.
09:00 CET - Perhaps the main event today is the second round in Abu Dhabi, where Elena Rybakina (25) and Paula Badosa (27) are among those taking to the court. Check out the full schedule here.
In Rotterdam meanwhile, Daniil Medvedev (28) and Hubert Hurkacz (27) will both be in evening action with Matteo Berrettini (28) and Felix Auger-Aliassime (24) beginning their campaigns before then.
We'll also keep you up to date with everything that happens in Dallas and Cluj.
07:57 CET - Hello and welcome to Flashscore's coverage of today's tennis!
Before we look ahead at what's to come today, there is some overnight news to bring you from the US, with Ben Shelton (22) advancing in Dallas with a 6-3, 6-3 win over Aleksandar Vukic (28) and Casper Ruud (26) beating James Duckworth (33) 7-5, 4-6, 6-2.