Lebanon's Hassan makes history with win over Eubanks in first round
Germany-born Hassan, ranked 170th in the world, won 6-4, 6-2 for one of the best victories of his career to fully vindicate being handed a Universality place by the ITF.
"I am unbelievably happy. We just enjoy it from the whole team. We are really proud and I'm also proud of myself," he told reporters.
"It was an unbelievable atmosphere. I was just trying to be calm because I didn't want to waste too much energy. When I won I could let it all out."
Hassan did not even set about becoming a professional until the age of 22, having previously played just for fun. But now he is living the dream as an Olympian and has a second-round clash against Argentina's Sebastian Baez to look forward to.
He has thrown himself into life in the athletes village, amassing quite a collection of pins. "I think the most special one is Japan because I'm a huge fan of Japan. I like watching a lot of animated mangas," he said.
Hassan was not the only Lebanon player in the draw as Hady Habib lost to French Open champion Carlos Alcaraz on Saturday
Hassan and Habib also lost in the doubles on Sunday.