(Photo credit: Geoff Burke-USA TODAY Sports)

Italian No. 4 seed Jannik Sinner beat Danish eighth seed Holger Rune -- and helped Novak Djokovic in the process -- to secure a round-robin sweep in the Green Group of the Nitto ATP Finals on Thursday in Turin, Italy.

Sinner took down Rune 6-2, 5-7, 6-4 to finish the group 3-0. The top-seeded Djokovic also advanced out of the group after outlasting Polish alternate Hubert Hurkacz 7-6 (1), 4-6, 6-1.

Had Rune beaten Sinner and Djokovic won, all three would have finished group play 2-1, and Sinner and Rune would have advanced thanks to owning the best set win percentages. Djokovic dropped a set when beating Rune and lost to Sinner in three sets before Thursday's match.

Instead, one of the greatest players of all time stayed alive and will play Saturday in the semifinals. Sinner's and Djokovic's semifinal opponents will be determined after the Red Group completes its round robin on Friday.

Sinner fired 11 aces without a double fault and saved four of five break points en route to beating Rune in a tight contest.

"For me, it was really important, resetting after the good win against Novak (on Tuesday)," Sinner said. "I never won against (Rune), so I really tried my best. I started off really well. In the second, he served better, he moved better, so it was a much more even match. The third set could have gone his way. At 4-3, I saved a break point. It was a little bit of a roller coaster today, but obviously really happy and happy to be in the semis."

Hurkacz replaced Greece's Stefanos Tsitsipas, who withdrew Tuesday due to a back injury. Hurkacz smashed 24 aces past Djokovic and saved five of seven break points, but Djokovic still managed to take him down, winning 22 of his 30 second-service points (73.3 percent).

The Serbian then had to stand by as his tournament fate was decided by the Sinner-Rune match.

"I was focused to win (my) match, so I did," he said at the time. "The outcome of tonight's match is not in my hands, that's it."

Nitto ATP Finals group standings (match win/loss, set win/loss):

Green Group

1. Jannik Sinner (3-0, 6-2) -- advanced

2. Novak Djokovic (2-1, 5-4) -- advanced

3. Holger Rune (1-2, 4-4) -- eliminated

4. Hubert Hurkacz (0-1, 1-2) -- alternate, eliminated

5. Stefanos Tsitsipas (0-2, 0-4) -- withdrawn

Red Group

1. Daniil Medvedev (2-0, 4-0)

2. Alexander Zverev (1-1, 2-3)

3. Carlos Alcaraz (1-1, 3-2)

4. Andrey Rublev (0-2, 0-4)