Jack Sock has snatched the last spot in the eight-man field for the season-ending ATP Finals with a win over Serbian qualifier Filip Krajinovic in the Paris Masters final.

The 16th-seeded Sock prevailed 5-7 6-4 6-1 to become the first American to win the singles title at the tournament since Andre Agassi in 1999.

Sock, who started the week in 24th position in the Race to London, needed to win the title to leapfrog Spain’s Pablo Carreno Busta to qualify for the November 12-19 event in London.

He did just that with a solid performance, wearing down the defence of world No.77 Krajinovic.

“I obviously snuck into … London unexpectedly so zero pressure on me to go there,” Sock said.

He is the first American man to make it into the singles draw of the elite season-finale since Mardy Fish in 2011.

“I’m going to swing big and play my game, like I always do, and just honestly enjoy the moment,” Sock said.

He won his first two service games to love but ran into a spot of bother in the sixth game when a double fault handed Krajinovic a break and a 4-2 lead.

Sock broke straight back but a fine forehand earned the Serb a set which he converted.

Krajinovic, however, lost his focus and a forehand error gave Sock an early break in the second set. The Serb fell 4-1 behind and could only break back once, allowing Sock to level at one-set all.

The momentum had shifted and Sock, who will finish the year as the American No.1 for the first time, raced through the deciding set to claim his maiden Masters title.

Despite the defeat, Krajinovic will climb to a career-high 33 in the rankings on Monday.

“I know that I will work even more right now. That’s for sure. Pressure is part of the sport,” the 25-year-old said.

” … if I want to be better, I have to handle that.

“So I will work on that also. So I hope next year will be better.”