The Italian needs to reach a maiden indoor championship to give himself a chance to earn the last ATP Finals berth up for grabs.

Meanwhile, Lorenzo Musetti is also through to the final four in the Greek capital, keeping his Turin hopes alive.

The Bjorn Borg group has Sinner, Zverev, Shelton and either Auger-Aliassime or Musetti, who are battling for the final spot.

And it's all up to the Italian—if he wins the title in Athens this week, he qualifies. Otherwise, the Canadian punches his ticket.

He's also a win away from the biggest title of his career.