Nitto ATP Finals 2019 semi-finalists: Rafael Nadal wins but Stefanos Tsitsipas advances to last four

Often the best yet, most frustrating thing about the ATP Finals is how everything is decided at the last minute. When Rafael Nadal, the World No. 1, took to the court yesterday for his last Round Robin stage match against Stefanos Tsitsipas, there was a cloud of doubt surrounding him.

Nadal's victory against the 21-year-old Greek would mean nothing if in the later match of the day, Alexander Zverev, the defending champion won. Almost true to the script, Rafael Nadal did win his match against Tsitsipas, in a hard-fought three-set thriller. The Spaniard regaled in the peace of ending the year as the World No. 1 for a record-equalling fifth time in his career while defeating the Greek in 6-7, 6-4, 7-5.

Rafael Nadal, the World No. 1

However, Nadal's win was not enough guarantee to grant him a spot in the semi-finals and set up a delicious date with Roger Federer, who was awaiting the winner of this match. The three-set victory by Nadal over Tsitsipas only gave way to further anticipation. It all ultimately depended on Alexander Zverev, who played the night match at the O2 Arena, against Daniil Medvedev.

A triumphant Alexander Zverev, through to his second consecutive semi-final in London.

Zverev, who has consecutively defeated Roger Federer, Novak Djokovic, and Rafael Nadal at the year-ending Championships, clashed against Daniil Medvedev in his last Round Robin encounter. Save for a defeat at the hands of Tsitsipas, it has been smooth sailing for the German, who has had a bittersweet year so far.

Things are finally looking up for the 22-year-old as he defeated the Russian in a convincing 4-6, 6-7 victory. With that, Zverev thwarted the chances of Rafael Nadal qualifying for the semi-finals of the tournament and doused the Spaniard's hopes of adding a maiden ATP Finals trophy to his long list of achievements.

Roger Federer, through to his 16th ATP Finals semi-final.

With Roger Federer already cruising into his 16th semi-final in London with a breathtaking win over arch-rival Novak Djokovic, the World No. 3 will now play tournament debutant Stefanos Tsitsipas for a place in the final. Tsitsipas, in his maiden outing at the tournament, has not dropped a single set in his matches against Medvedev and Zverev, although he squandered two to Nadal.

Dominic Thiem, through to his first semi-final in London

Dominic Thiem, on the other hand, under his new coach is in superb form currently. He defeated both Djokovic and Federer after falling prey to Italian challenger Matteo Berrettini, in the Round Robin stages. For Thiem, this would be his first semi-final in London as he prepares to meet Zverev, the defending champion from last year. The fireworks are ready to sizzle as the four semi-finalists promise to bring the show down on Saturday night!