Sixth-seeded Tsisipas, 21, beat fifth-seeded Thiem, 25 with the score 6-7 (6-8), 6-2, 7-6 (7-4).
¡#TSITSIPAS CAMPEÓN DEL MASTERS DE #LONDRES!— Notimix #Deportes (@NotimixDeportes) November 17, 2019
El griego de 21 años remontó un partidazo y se impuso por 6-7 (6), 6-2 y 7-6 (4) al austriaco #Thiem. En semifinales había eliminado a #Federer pic.twitter.com/mUtMiwIJR1
The match, which was held at the O2 Arena in London, lasted 2 hours 36 minutes.
This was the debut of Tsisipas in ATP Finals.
The ATP Finals, in which eight top-ranked players take part, is the fifth most important tennis tournament after the four Grand Slams. Unlike most other tennis tournaments with knock-out system, it consists of a group stage, semifinals, and the final match.