Jannik Sinner is already world number 1 and has 2 Grand Slams at 23

New US Open champion Jannik Sinner is making big strides in a short amount of time.

And that, he figures, bodes well for what's to come.

Just 23, Sinner already reached No. 1 in the ATP rankings a few months ago and, on Sunday, collected the second Grand Slam trophy of his career and of the year by defeating Taylor Fritz 6-3, 6-4, 7-5 in the final at Flushing Meadows.

Add that to his Australian Open in January, and Sinner is the first man since Guillermo Vilas all the way back in 1977 to pick up major titles No. 1 and No. 2 within the same season.

I've gone through a lot things quickly, said Sinner, Italy's second US Open singles title winner, joining 2015 women's champ Flavia Pennetta. I'm still young. That gives me confidence I still can get better, because at 23, you haven't perfected everything. So my team and I know we have to improve.

In what ways? He pointed to the match against Fritz.

Today, I played well from the back court. I felt good there, said Sinner, who was ...