Jannik Sinner shrugged off lower back pain on Thursday to defeat Holger Rune 6-3 5-7, 6-4 to win the Green group with a perfect 3-0 record at the ATP Finals.
The Italian advanced to the Saturday semi-finals with Novak Djokovic benefitting from the magic of round-robin mathematics to squeeze into the final four after defeating Hubert Hurkacz earlier in the day in Turin.
Had Rune won, he and Sinner would have advanced out of the group, leaving the senior Serb stranded on third place.
Sinner looked to be dealing with lower back pain at the midway point as he dropped the second set but never called for the trainer.
The first Italian man to win 60 matches in a season secured a late break in the third set to ice his win in front of 13,000 home fains at the Pala Alpitour.
“It was really, really important to get another good win after beating Novak (on Monday),” the winner said.
“The third set could have gone his way, it was a bit of a roller-coaster.
“But I’m happy to be in the semi-finals, it means a lot to win here in Italy. I’m happy I have a chance to play another match.”
Sinner advanced with 33 winners over the two-and-a-half-hour battle.