(Photo credit: Robert Deutsch-Imagn Images)

Italian star Jannik Sinner is through to the semifinals by taking down a familiar opponent, Germany's Alexander Zverev, in their second match of Bjorn Borg Group play at the Nitto ATP Finals on Wednesday in Turin, Italy.

Defending champ Sinner improved to 2-0 in the group stage with straight-sets wins over both players that stand at 1-1, Zverev and Felix Auger-Aliassime. The Canadian Auger-Aliassime defeated Ben Shelton in the other match of the day, ensuring Sinner will have a spot in the semifinals for the third straight year.

Sinner took down Zverev 6-4, 6-3. It was the third time in 17 days that the pair faced off. Sinner beat Zverev in the final of the ATP 500 tournament in Vienna, then again in the semifinals of the ATP 1000 event in Paris.

This one was closer than that Paris meeting that Sinner took 6-0, 6-1.

'A very, very competitive match, a very close match,' Sinner said in his on-court interview. 'I felt like I was serving very well in important moments. I tried to play the best tennis possible when it mattered, which fortunately went my way.'

Sinner fired 12 aces without a double fault en route to winning 40 of 48 first-service points (83.3%). He faced seven break points and saved all seven, three of them coming in a single game when trailing 2-1 in the second set to rally from down 0-40.

'We both changed a little bit tactically, so I felt like we both were trying to hit quite fast, quite flat,' Sinner said. 'But I'm very happy with how I returned his serve. It's very difficult. (Zverev has) one of the best serves in the game.'

Elsewhere, Auger-Aliassime stayed alive after his 7-5, 6-1 loss to Sinner in the first match of his second appearance at the tournament.

Auger-Aliassime rallied to beat Shelton 4-6, 7-6 (7), 7-5 in a two-hour, 25-minute affair.

The two men held serve throughout the second set before Auger-Aliassime took an early three-point lead in the tiebreaker. Shelton charged back and tied it at 6-6 and 7-7 before his opponent got the better of him.

Shelton saved 5 of 7 break points, including two match points in the third set before Auger-Aliassime broke through on his third opportunity.

'I was able to play 2 1/2 hours of high-intensity tennis,' Auger-Aliassime said. 'I have to give him credit, he kept coming up with great serves. When the opponent plays that well, you have to give him credit, but also to myself for staying cool.'

Auger-Aliassime will have to keep his cool again Friday when he faces Zverev to conclude the group stage. The winner will receive the second berth from the Bjorn Borg Group into the knockout round. Sinner will also face Shelton that day.

--Field Level Media