Italian top seed Jannik Sinner produced a spirited comeback to defeat Germany's Alexander Zverev 3-6 6-3 7-5 in the Vienna Open final on Sunday, securing his fourth ATP Tour title of the season and his second triumph in Austria's capital.

Sinner, who beat Zverev in straight sets at this year's Australian Open, has now won 21 consecutive matches on indoor hardcourts. The 24-year-old has now also notched 22 tour-level titles and 51 career wins against fellow top-10 players.

The world number two banged down 11 aces and unleashed 44 winners in a thrilling contest that lasted two hours and 28 minutes.

"It feels amazing," Sinner said. "It was such a difficult start in the final for me. Down a break ... I had some chances in the first set, couldn't use them. He was serving very well.

"I tried to stick there mentally. Trying to play my best tennis when it counts. Third set was a bit of a roller-coaster. I was feeling very well the ball at times. I tried to push.

"Very happy to win another title. It's very special."

The win also allowed the four-times Grand Slam champion to level his head-to-head record against Zverev at four wins apiece.

"I'd like to congratulate Jannik, whose level has been off the charts these last two years," Zverev said. "Currently for me you're the best player in the world.

"What an amazing year. Four Grand Slam finals and two Grand Slam titles. This week of course, simply the best player here in Vienna..."

World number three Zverev saved a break point to hold the opening game before getting a break over Sinner to go 3-1 up in the first set. Zverev won the set 6-3, landing four aces while Sinner had two, with the 28-year-old German dominating the rallies.

Sinner fought back in the second set, outwitting Zverev with a crosscourt dropshot to get his first break, going 2-0 up.

The Italian was more in control of the rallies, making his opponent chase forehands near the sidelines as Zverev won only two points in the last two games the Italian served on his way to securing the set 6-3.

The deciding set was a gripping battle as both players exchanged blows, with the score locked at 4-4. Sinner appeared to be struggling with cramp in his left hamstring during the seventh game of the set, but he refused to back down.

Zverev briefly looked set to seize victory after edging ahead 5-4, but Sinner dug deep to level the match before producing a crucial break for 6-5. Sinner then held his nerve to serve out the match and secure his second title in Vienna.

"Yeah it was very difficult, of course," Sinner said.

"Most important is trying to not give up. Trying to stay there. Trying to see what the situation is. I just tried to make the right choices at the right time. I think that was the key today.

"Serving well, saving energy in my service games was important too. It was a very great performance from me, but I feel like it was from both sides."