Stefanos Tsitsipas broke his hoodoo against Daniil Medvedev on Monday as Rafael Nadal prepared to launch his bid for a first ATP Finals title with questions over his fitness.

The Greek 21-year-old came into the match at London’s O2 Arena with a 5-0 losing record against his Russian opponent weighing on him.

But he edged a tight first set, winning the tie-break, and a single break late in the second set proved decisive in a 7-6 (7/5), 6-4 victory.

There was little to choose between the players in a match dominated by serve but Medvedev fatally chose to leave a ball in the ninth game of the second set that landed in, handing Tsitsipas a break point which he seized, going on to wrap up victory.

The pair have a spiky relationship.

Tensions flared between them at the 2018 Miami Open and Tsitsipas recently labelled Medvedev’s way of winning as “boring” after defeat against the Russian in Shanghai.

World number four Medvedev is looking to add lustre to an impressive breakout year by winning the glitzy end-of-season event in London.

The 23-year-old Russian has emerged as the leader of the pack of young tyros preparing to unseat the old guard of Nadal, Novak Djokovic and Roger Federer.

Four of the eight competitors at the ATP Finals at the O2 Arena are under 24 for the first time in 10 years.

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.

The Spanish top seed is locked in a battle with Djokovic to finish as the year-end number one.

Regardless of Djokovic’s results this week, Nadal will clinch the year-end top spot for a fifth time if he reaches the final with a 4-0 record.

Nadal has qualified 15 straight times for the year-end championships but he has only made eight prior appearances due to injuries.

Djokovic launched his bid for a sixth ATP Finals title with a comfortable win against Matteo Berrettini on Sunday but Federer slipped to a straight-sets defeat against Dominic Thiem, putting his hopes of progress in serious jeopardy.