Jack Sock upsets Alexander Zverev to reach the ATP Finals last four

Jack Sock joined Boris Becker group winner Roger Federer in the semi-finals of the ATP Finals on Thursday, after upsetting Alexander Zverev in a thriller.

Six-time champion Federer finished the round-robin stage with a three-set win over Marin Cilic at The O2 earlier in the day and world No 9 Sock went through in second position with a 6-4 1-6 6-4 success over Zverev.

Zverev failed to find any rhythm with his forehand early on and looked to be suffering some early jitters. It came as no surprise when he was broken in the seventh game.

Sock, 25, consolidated his advantage by saving three break points with some monster serving to close in on the first set, which he successfully served out thanks to a deft winner at the net.

The German, who has won five tournaments this year, including two Masters 1000 titles, began to swing freely in the next and unlocked Sock with a quick-fire double break to take control and send the match into a final-set shoot-out.

Some incredible defence from the 20-year-old gave him the early advantage, but a sudden collapse allowed Sock a way back in with a double break and a commanding 4-1 lead.

In a fluctuating see-saw battle, world No 3 Zverev dug deep with his never-say-die attitude coming to the fore, as he slowly reeled Sock back in to level at 4-4.

But Sock showed his mettle to see off his opponent by taking his first match point to become the first American since Andy Roddick in 2007 to reach the final four of the season-ending tournament, and now faces Grigor Dimitrov.

Shot of the match

Rollercoaster ride for Sock

"That was a rollercoaster match for sure," said Sock. "I was down some break points early but able to fight that off in the first set. He played really well in the second – he served really well and dictated the points. I didn’t have a hot start to the third set but it has been a theme to hand in there the past few weeks and keep fighting. You never know what can happen.

And on his semi-final opponent, Dimitrov, he said: "He has played some incredible tennis – winning his last match [against David Goffin] fairly comfortably. He has had an amazing 2017 so once again I am going to have to play some of my best tennis to win. We have played numerous times before so we both know each other well and it should be a fun match."

Experts’ view

What’s next

Sock will face Pete Sampras group winner Dimitrov in the semi-finals on Saturday where he enjoys a 3-1 head-to-head record. You can watch both semi-finals live on Sky Sports, with the action getting underway from midday.

The season-ending extravaganza ATP Finals ends another memorable year which will be covered via our website www.skysports.com/tennis with live blogs, reports, reaction and expert analysis as the season reaches its climax.

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(c) Sky News 2017: Jack Sock upsets Alexander Zverev to reach the ATP Finals last four