Expectations have long followed Alexander Zverev, with few people doubting that he is destined for stardom on the ATP World Tour. So it wasn’t a complete shock that the 20-year-old German soared up the Emirates ATP Rankings from No. 24 at the end of last year to third in the world now. His five titles and two ATP World Tour Masters 1000 trophies (Rome, Montreal) this season cemented his status as one of the sport’s best.

But Zverev did not finish his 2017 on a high note. He advanced to just one semi-final in his final seven tournaments of the year. And when playing Jack Sock on Thursday evening for a spot in the final four of the Nitto ATP Finals, Zverev let slip a break in the third set, failling to the American. Zverev was brutally honest about the loss.

“I choked,” Zverev said. “Won the second set 6-1. I was 1-0 [in the third set] with a break. He got a point penalty. I was down 1-4 within 10 minutes where I didn’t put many balls in the court. When I got back at 4-5, that’s one of the worst games I think I played all year. So, yeah, I just choked.”

Early in the third set, it seemed that Sock was unraveling, not Zverev. The eighth seed launched his second ball of the night into the stands after getting broken to begin the set, earning himself a point penalty. On the other side of the court, Zverev was emoting positively and seemingly in a rhythm from the baseline.

And then he wasn’t. One lapse of concentration was all it took, as he handed the break back to Sock. And while the third seed managed to get back on serve later in the set, an ugly double fault, which Zverev described as “about a 19 mile-an-hour serve that I hit in the bottom of the net” gave the 25-year-old across from him match point, which Sock would not waste.

“I found my rhythm again in the middle of the third set. I got the break back. I started to play I feel like better until the game of 4-5,” Zverev said. “That was one of the worst games I think I played [this year], not only in this match.”

But nevertheless, the stinging defeat does not take away from the tall right-hander’s success this season. He became the youngest in the Top 3 of the rankings since Novak Djokovic (20) in 2007 and also the youngest player to win five or more titles in a single year since Djokovic, also in 2007. The last German to accomplish those feats was Boris Becker. Djokovic has won 12 Grand Slam titles, and Becker six.

So sure, Zverev is happy with the progress he has made. But he is not happy with his close to the season.

“It’s been an awesome year,” Zverev said. “Still, the end of the year was absolute crap for me. If I would have played the whole year like I did, by the end of the year I don’t think I would have finished Top 50.”

It is said that many people are their own toughest critics. Sock had nothing but positive things to say about Zverev’s performance this year.

“The guy is 20 years old. He’s played some absolutely outstanding tennis in his career. I mean, can’t even legally drink a beer in the U.S. and he’s three in the world, playing like he is,” Sock said. “ It could be the expectations for him, as well. Obviously with the tennis he’s played, not only this year, but the start of his career, he could go out there and expect himself to play a certain way.”

Now, Zverev will have an opportunity to work on his game so that next year, he will not only be able to raise his level, but maintain it consistently. He will be going to the Maldives for his brother Mischa’s wedding, and then getting right back to work.

“I’m going to do three weeks of physical [training] again, then start tennis, just do all the basic stuff again,” Zverev said. “[I want to] try to get back to where I was [at the] beginning of the year, try to maybe improve even more.”

As for his sour final match to close what was an extremely impressive 2017, Zverev had no excuses.

“It was just nerves, nerves getting in the way,” Zverev said. “They got the better of me.”

Everything was pointing against Jack Sock on Thursday night at the Nitto ATP Finals.

After winning the first set against World No. 3 Alexander Zverev, the American had disappeared in the second, losing it in only 28 minutes. To start the decider, Sock had fallen behind a break and received a point penalty for smashing a ball off the court.

Zverev stepped up to the service line leading 1-0, 15/0, and with all the momentum at his back. The match looked as if it’d be over in minutes.

But Sock, just as he had done earlier this month at the Rolex Paris Masters, came back from near-certain defeat and will now play in the semi-finals of the Nitto ATP Finals for the first time. The eighth-seed debutant upset Zverev 6-4, 1-6, 6-4 at The O2 in London to become the first American to reach the final weekend of the season since Andy Roddick in 2007 (l. to Ferrer).

“I’m playing with house money. I’m going out there and letting loose, having fun, trying to put on a show a little bit, just enjoy my time,” Sock said. 

The 25-year-old finishes second in Group Boris Becker, behind group winner Roger Federer, and will face Grigor Dimitrov, who won Group Pete Sampras, on Saturday. Sock leads their FedEx ATP Head2Head series 3-1, including a three-set fight earlier this year at the BNP Paribas Open in Indian Wells in which Sock saved four match points, including three consecutively from 0/40, to advance.

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“He got me early on when we played. I’ve been able to get some wins against him. Obviously I think he’s a little bit different player since the last time I played him. I think he’s really found his game, what exactly he wants to do out there. It’s showing throughout the year. He’s playing deep into tournaments almost every week, really establishing himself in the Top 10,” Sock said.

“But once again, I’m playing with a lot of confidence as well, coming off Paris, playing here, winning some of my matches, getting into the semis.”

Sock started against Zverev with the same aggressive mindset that helped him beat Dimitrov in Indian Wells. The American was blasting forehands and landing 130 mph-plus first serves. He was also avoiding backhand-to-backhand battles with Zverev, who possesses one of the game’s best backhands.

Sock saved all six break points and broke Zverev in the seventh game before serving out the set. Zverev, however, blitzed through the second, and the 20-year-old German looked as if he’d become the youngest semi-finalist at the Nitto ATP Finals since 20-year-old Rafael Nadal in 2006.

But at 1-0, 15/0, Zverev tossed in a loose service game, double faulting twice and dumping a forehand into the net on break point. Suddenly, Sock had the momentum again, and he overcame a late break to celebrate the biggest win of his career. At 4-5, 30/30, Zverev double faulted – his eighth of the match – and on match point, Zverev, who had won five ATP World Tour titles this year, sprayed a forehand wide.

“I choked. It’s quite easy. Won the second set 6-1. I was 1-0 with a break. He got a point penalty. I was down 1-4 within 10 minutes where I didn’t put many balls in the court,” Zverev said. “So, yeah, I just choked.”

It’s the second Top 5 win of Sock’s career. His first came earlier this year during the semi-finals of the BNP Paribas Open, where he dismissed No. 5 Kei Nishikori in straight sets to reach his first ATP World Tour Masters 1000 semi-final.

And to think, on 1 November, Sock was No. 22 in the Emirates ATP Rankings and a game away from heading home for the off-season. The American was down 1-5 in the third set against Brit Kyle Edmund. But Sock climbed back to win 4-6, 7-6(4), 7-6(5) and extend his season. He qualified for the Nitto ATP Finals by winning the Rolex Paris Masters (d. Krajinovic), his first Masters 1000 title.

“If I put pressure on myself, I probably wouldn’t be here in the first place. I think getting through that first match in Paris, playing Edmund, honestly I should have lost, but ended up winning the tournament. I don’t think I would have gotten through that week if I put pressure on myself,” Sock said.

“Then to come here, sneak in the last spot. I’m going to have fun, play big, play free, like you just said. That’s definitely not going to change. No one expected me to be here in the first place.” 

On Saturday, he’ll try to prolong his season one more day, until Sunday, the final day of the 2017 ATP World Tour season.

Ryan Harrison and Michael Venus arrived at The O2 with little to no momentum from the end of their regular season, losing five of their final six matches.

But that has not mattered this week at the Nitto ATP Finals. Harrison and Venus finished round-robin play with a perfect record on Thursday, defeating third-seeded Jean-Julien Rojer and Horia Tecau 6-3, 7-6(5).

The American-Kiwi pairing has won Group Eltingh-Haarhuis, and will play the second qualifier from Group Woodbridge/Woodforde in Saturday’s semi-finals.

Rojer and Tecau, the 2015 Nitto ATP Finals champions, finished their season finale 0-3. It is the second time in three appearances in London that this year’s US Open champions have gone winless at The O2, with their career record at the event falling to 5-6.

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In the early going, it looked like the Dutch-Romanian team would earn their first victory of the tournament, breaking serve at 2-2. But they could not hold the advantage, losing the final four games of the opener. The eighth seeds proved to have too much power, especially Harrison with his overwhelming serve and forehand, which dominated in the key moments.

There was only one break opportunity in the second set, so the two sides went to a tie-break. And after capturing a mini-break to catapult to a 4-1 lead, it seemed that Rojer and Tecau would force a decider. But at 5-3, Tecau let a Harrison volley go, incorrectly thinking it might sail long. After Harrison claimed two points on his serve to earn match point, the American split his opponents with a lasered backhand to seal the triumph.