Stefanos Tsitsipas defeated Daniil Medvedev for the first time in six meetings in their opening match at the year-ending ATP Finals, the Greek prevailing 7-6 (5), 6-4 at the O2 Arena in London on Monday.

Strong serving from both players in the opening set – Medvedev faced one break point, Tsitsipas none – ensured a tiebreak, which Tsitsipas inched ahead to take 7-5.

Tsitsipas looked the stronger player as the second set began. Medvedev saved two break points at two-all, but was unable to save one when serving at four-all, giving Tsitsipas the chance to serve for the match.

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Tsitsipas, the world No. 6, had lost five consecutive times to Medvedev, though all of their encounters have been close – the only straight-sets victories for the Russian coming at the Shanghai Masters in October.

Tsitsipas’s year has tapered off after a strong start in January, where he beat Roger Federer in the fourth round of the Australian Open; his run to the semifinals at Melbourne saw him win as many matches – five – as he did at all four Grand Slams in 2018. After two wins from four finals in the first five months of 2019, he’s only reached one more final since, at the China Open in October, losing to Dominic Thiem.

Medvedev has had an outstanding year on the ATP Tour, reaching six consecutive tournament finals, including the US Open, where he lost to world No. 1 Rafael Nadal, and three Masters 1000 tournaments. Beginning the year at world No. 16, he ranks just behind the Big Three of Rafael Nadal, Novak Djokovic and Federer, and holds a chance of overtaking the Swiss maestro this week.

Tsitsipas and Medvedev are placed with world No. 1 Rafael Nadal – who’s seeking a first ATP Finals title – and Alexander Zverev in Group Andre Agassi. Novak Djokovic, Federer, Dominic Thiem and Matteo Berrettini make up Group Bjorn Borg.