John Millman will be the first man to try to stop Alexander Zverev claiming back-to-back titles in Cologne, while Jannik Sinner also won.
Aryna Sabalenka will face Coco Gauff in the second round of the Ostrava Open after the 16-year-old American defeated Katerina Siniakova.
Seeds made early exits in Antwerp and Cologne as Frances Tiafoe and Steve Johnson claimed unexpected wins.
Anett Kontaveit, Sara Sorribes Tormo, Maria Sakkari and Barbora Krejcikova booked their places in the second round of the Ostrava Open.
A victory on home court at the St Petersburg Open means Andrey Rublev will scale new heights in the ATP rankings on Monday.
Andy Murray is struggling for form and fitness, and the latter has caused him to withdraw from the Cologne event that starts on Monday.
Alexander Zverev won the Cologne Indoors, his first 2020 title, as Felix Auger-Aliassime's wait for Tour glory goes on.
Marco Cecchinato lost to Laslo Djere in a competitive final in Sardinia that lasted nearly two hours and 20 minutes.
The St Petersburg Open final will see Andrey Rublev face Borna Coric, who is through to the showpiece for the second successive year.
Andrey Rublev and Denis Shapovalov will fight it out for a place in the final of the St. Petersburg Open on Saturday.