16:19 CET - After just under three hours, Tomas Martin Etcheverry has claimed a 6-7, 7-6, 6-3 win over American qualifier Mackenzie McDonald in Athens.
15:59 CET - Defending champion Coco Gauff is a set to the good in her must-win clash against Jasmine Paolini at the WTA Finals. The American took it 6-3 in 40 minutes.
Elsewhere, Daniel Altmaier is through in Metz after a solid 6-4, 6-4 win over sixth seed Arthur Rinderknech, while qualifier Yannick Hanfmann has advanced in Athens.
14:42 CET - The first match of the day in Metz was an all-French affair, and it's been won by lucky loser Kyrian Jacquet, who has beaten Luca van Assche 4-6, 6-3, 6-4.
This was the first ATP win of Jacquet's career.
10:36 CET - Today's headline action comes at the WTA Finals in Riyadh, where defending champion Coco Gauff faces Jasmine Paolini at 15:00 CET, with both players needing a win after defeats in their opening matches.
Following that clash, the other game in the Stefanie Graf Group sees world number one Aryna Sabalenka take on Jessica Pegula, as both women target a spot in the semi-finals.
Elsewhere, there's plenty of action at ATP events in Metz and Athens, with Novak Djokovic, Flavio Cobolli and Cameron Norrie among the standout names involved.
Check out the full schedules in Metz and Athens via the links.
10:00 CET - Good morning and welcome to our coverage of today's tennis in Riyadh, Metz and Athens!