London - Stefanos Tsitsipas hailed one of the "most important victories" of his career after breaking his hoodoo against Daniil Medvedev on Monday as Rafael Nadal prepared to launch his bid for a first ATP Finals title.
But at 5-5 in the breaker, Tsitsipas produced one of best points of the match and finished it with a forehand volley winner. He converted the opportunity with an aggressive forehand and let out a roar of delight.
The two players have a spiky relationship.
"I had great support, there are Greek flags everywhere, it feels like I'm playing in Athens," he added. "I had goosebumps."
Nadal, takes on defending champion Alexander Zverev in the later match in Group Andre Agassi with major questions over his fitness since he withdrew injured from the Paris Masters at the semi-final stage.
Nadal has qualified 15 straight times for the year-end championships but he has only made eight prior appearances due to injuries.