Russian Nikita Salamatov, 26, and his 25-year-old Ukrainian wife Anastasia Dudnikova were attacked at the helipad in a park on Phra Tamnak hill in Chon Buri province about 1am. The man was bleeding from a head wound and his wife had a cut inside her mouth when authorities arrived.
Police found two glasses, a broken wine bottle and a flower vase at the scene.
The tourists had turned over a cement bucket to use as a makeshift table and brought flowers and wine for their romantic interlude when several attackers hit them and made off with their 2,000 baht, $300 and a Nokia mobile phone.
Defence volunteers who gave them first aid said they had just patrolled the area and warned the couple to leave due to possible late-night danger, but the tourists asked to stay a bit longer.
Police were examining surveillance-camera footage to try to identify the assailants.