19:40 CET - Alejandro Davidovich Fokina is through to the final in Basel after his opponent Ugo Humbert was forced to retire with injury, while the Spaniard was leading 7-6(4), 3-1.
That's it for today's action! Tune back in tomorrow for our coverage of all four finals in Vienna, Basel, Tokyo and Guangzhou.
19:11 CET - Second seed Alexander Zverev will face top seed Jannik Sinner in tomorrow's Vienna showpiece after the German battled through a competitive second set to defeat Lorenzo Musetti 6-4, 7-5.
17:53 CET - Alexander Zverev is one set away from joining Jannik Sinner in the Vienna final, with the German leading Lorenzo Musetti 6-4 after 50 minutes.
17:11 CET - Joao Fonseca makes history! The 19-year-old has become the Brazilian ever to reach an ATP 500 final thanks to a 7-6, 7-5 win over Jaume Munar that he sealed in just under two hours.
If he wins tomorrow, only Carlos Alcaraz will have become an ATP 500 champion at a younger age, and the Brazilian will also make his debut in the world's top 30.
16:35 CET - Jannik Sinner has absolutely stormed into the final in Vienna, beating Alex De Minaur 6-3, 6-4 in under an hour and a half in the Austrian capital.
With his 47th win of the year, the Italian moves into his eighth final of the year, and now has 20 victories on indoor hard courts in a row.
14:50 CET - Today's ATP action is about to start, and it's starting in style, with Jannik Sinner taking on Alex De Minaur in the first Vienna semi-final.
Over in Basel, young star Joao Fonseca is looking to reach the biggest final of his career yet in his clash with Jaume Munar.
Let the games begin!
14:23 CET - In a big disappointment for home fans in Guangzhou, China's Shuai Zhang has retired from her semi-final while 5-2 down in the first set, meaning second seed Ann Li of the USA moves into the final.
12:42 CET - Lulu Sun is through to the showpiece event in Guangzhou, with the New Zealander battling through a tight second set to beat Claire Liu 6-0, 7-6(3).
08:29 CET - Belinda Bencic has booked her spot in tomorrow's Tokyo final after recovering from a second-set wobble to defeat Sofia Kenin 7-6(5), 3-6, 6-2.
07:43 CET - Fifth seed Belinda Bencic and American Sofia Kenin are currently on court for their semi-final clash in Tokyo, with the Swiss player in the driving seat after taking the opening set.
Follow the match with Flashscore here.
In the other semi-final in Japan, Elena Rybakina has withdrawn because of problems with her back, meaning Linda Noskova is through to tomorrow's showpiece.
07:30 CET - Good morning and welcome to our coverage of today's tennis!