Jack Sock beat Filip Krajinovic 5-7, 6-4, 6-1 Sunday to win the Paris Masters and qualify for the season-ending ATP Finals.

It was the 16th-seeded American's third title of the year, fourth overall and first at a Masters. It sends him through to the finals in London for the first time. He will break into the top 10, climbing to ninth.

"Incredible week. Hard to describe, honestly. I don't think it's really hit or soaked in yet," said Sock, who was one game away from losing in the second round. "To come back from the deficit I was down and to have this trophy next to me now has been an incredible achievement."

He sealed victory on his first match point when Krajinovic, a Serbian qualifier ranked No. 77, sent a backhand long. Sock fell onto his back with his hands on his face, then jumped into the seating area to celebrate with his team.

"I had some anxious sleep last night," Sock said. "I was able to find that groove in the second and third [sets] and kind of turn things around."

He is the first American winner here since Andre Agassi in 1999; and the first American winner of a Masters tournament since Andy Roddick at Miami in 2010.

"I've had a rough season pretty much since, since March," Sock said. "Coming in this week I had no idea I could even make London. It wasn't in my head. I just wanted to play some good tennis my last week and go start my off-season."

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Filip Krajinovic of Serbia, left, and Sock pose with their trophy after the final of the Paris Masters. (Michel Euler/Associated Press)

With a wry smile, Sock said he would be celebrating the biggest win of his career with "just a water on the rocks."

Krajinovic was the first qualifier in a Masters final since Jerzy Janowicz, also here, in 2012.

After losing, the 25-year-old Serb sat slumped in his chair, shaking his head in disappointment.

He had only played finals on the challenger circuit before, winning all five of them, and came through the qualifying rounds. He seemed to run out of energy in the third set, which Sock controlled completely.

"I was not aggressive enough. I have to be against him," Krajinovic said. "He started to play better and better and I didn't serve well."

Still, Krajinovic will climb to No. 33 next week.

Sock's other titles this year were at Delray Beach, Florida and Auckland, New Zealand — both on outdoor hard courts.

This one gives him a winners' check of almost $1 million US and a ticket to London.