13:53 CET - Miami finalist Lehecka has narrowly avoided the fate of Medvedev and Rublev, with the 11th seed fighting back from a set down to beat Alejandro Tabilo 4-6, 7-6 (4), 6-3 in a gruelling battle that lasted just under three hours.
Zverev is now in need of a comeback of his own, with the German losing the opening set of his clash with Garin 6-4.
12:31 CET - Another shock result! Former Monte Carlo champion Rublev is out, with world number 47 Zizou Bergs beating him 6-4, 6-1.
There wasn't too much between them on the whole, with Rublev facing nine break points and Bergs eight, but the Russian was only able to convert one while the Belgian took four of his chances, and that made all the difference.
12:06 CET - Wow, what a start to the day this is. Indian Wells runner-up Medvedev has been absolutely destroyed by Berrettini, losing 6-0, 6-0 to the Italian in under an hour.
The Russian produced a disastrous display, making five double faults and 27 unforced errors, and winning just a quarter of the points played. As is often the case, he made no effort to hide what he thought of his performance, launching his racket at the wall in frustration at one point.
On the flip side, Berrettini was near-flawless and dubbed it the best match of his career in his post-match interview. He becomes just the fifth man to defeat a top-10 opponent 6-0, 6-0 since the ATP rankings were introduced in 1973.
Berrettini is a much better player than his current ranking would suggest and perhaps the better of the two on clay, but that's still a remarkable result.
09:00 CET - Good morning and welcome to our coverage of the Monte Carlo Masters on what promises to be a thrilling day in Monaco!
Play gets started in a couple of hours at 11:00 CET, as seventh seed Daniil Medvedev faces Italy's Matteo Berrettini, while 2023 champion Andrey Rublev and Miami runner-up Jiri Lehecka are also in early action.
The highest seed taking to the court today is third seed Alexander Zverev, with the German coming up against Chile's Cristian Garin. That match is due to get underway around 12:30 CET.
Elsewhere, clay-court specialist Casper Ruud faces mercurial Frenchman Corentin Moutet, last year's runner-up Lorenzo Musetti meets Valentin Vacherot, and sixth seed Felix Auger-Aliassime takes on experienced Croat Marin Cilic.