The Spaniard, whose haul of 86 singles titles includes just one on indoor hard courts, is chasing the biggest prize missing from his resume at the eight-man elite event.
Nadal, 34, has qualified for the ATP Finals for a record 16 consecutive years but has been forced to withdraw on six occasions. The second seed won his opening round-robin match against Andrey Rublev but defeat against Dominic Thiem meant he faced a shootout against 2019 champion Tsitsipas to reach the semi-finals.
Nadal sets up a semi-final against Daniil Medvedev as he bids to round off the COVID-19-interrupted season in style. “In general terms a very positive match for me,” said Nadal.
“To be in the semi-finals here at the last tournament of the year is an important thing. Happy for that and looking forward to the semi-finals against Daniil.” He added: “It’s always difficult to play here against the best players of the world every single day, end of the season and most of the time you get here a little bit tired but this year is a little bit different.”