© Peter Staples/ATP World Tour

Jack Sock picks up his first win at the Nitto ATP Finals in London by defeating Marin Cilic in three sets.

Sock Gains First Win In London

First American singles player to win at season finale in 10 years

All match long on Tuesday at the Nitto ATP Finals, Jack Sock had been content to slice his backhand to Marin Cilic in hopes of seeing a better option – a chance to crush his world-class forehand.

But with the match on the line, the eighth seed ditched the plan and was bold – swinging through his two-handed backhand with power. His reward: his first win at the Nitto ATP Finals.

The 25-year-old American beat fifth seed Marin Cilic 5-7, 6-2, 7-6(4) to move to 1-1 in Group Boris Becker and improve his hopes of reaching this weekend's semi-final round.

“I think if I do the right things and I play the right tennis, I can give myself a chance to play on the weekend of any tournament. I think I've showed that more this year,” said Sock, who won three ATP World Tour titles this season, including the Rolex Paris Masters earlier this month.

The Nebraska native became the first American singles player to win at the Nitto ATP Finals since Andy Roddick 10 years ago today in Shanghai. Both Roddick (2010) and Mardy Fish (2011) had gone winless during their season finale appearances in London. “I've been talking to Mardy since I've been here. He told me to enjoy it,” Sock said.

Sock also had fallen in the British capital, dropping his opener to second seed Roger Federer in straight sets on Sunday. He risked falling into an 0-2 hole at the season finale. But the American played big and free against Cilic, and especially with the match in the balance.

Sock fell behind a mini-break in the third-set tie-break, and the match looked in doubt as Cilic prepared to serve up 4/3. He had won 15 consecutive points on serve, and if the trend continued, the Croatian would lead 6/3 and be a point away from registering his first win of the week.

Sock, though, played his best tennis, bunting a winner that had trickled off the net cord for 4/4. He also benefitted from a loose Cilic backhand to take both points on the Croatian's serve. With the match on his racquet, the American played even braver, smacking a backhand up the line that Cilic couldn't handle. On match point, Sock belted a forehand that Cilic returned long.

That tie-break, it was quite a few close points. Him getting that unbelievable [net] cord, one backhand down the line that he hit on 5/4. He didn't hit many down-the-line winners during the match. That was a big shot to hit at that stage,” Cilic said.

I think Jack is playing really good. He had a really nice season, especially the beginning, now the end... Overall I think he's playing good tennis, quite aggressive. When he's playing well, he's definitely very dangerous.”

Sock, the World No. 9, improves to 3-0 against Cilic in their FedEx ATP Head2Head rivalry. All three wins have been milestone victories for the right-hander.

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Sock came back from two sets down in July 2016 during a Davis Cup rubber, and Sock beat Cilic in straight sets during the 2016 US Open to reach the fourth round of his home Grand Slam for the first time.

Tuesday was another career moment for Sock, who will look to go to 2-1 in London when he faces Germany's Alexander Zverev on Thursday.

For Cilic, it's another heartbreaking loss at The O2. The fifth seed, who's making his third appearance at the season finale, was looking to bolster his chances of making the semi-finals for the first time. The Croatian fell to third seed Alexander Zverev on Sunday after leading by a break in the third set.

Cilic led Sock by a break in the third set as well, 3-0, before the American rallied.

“Definitely disappointing in both matches in that third set, being in a good position, putting myself in a good position. But unfortunately I didn't close it,” Cilic said.

“What makes the difference I think with these top guys, if you don't take the chances, it's one point here and there. [I'm] just going to try to be a little bit more stubborn in my preparations maybe for the next match, and hopefully next year. Hopefully I'm going to perform better.”