Jack Sock pips Marin Cilic in final-set tie-break

The American fought back from a set down, and a 3-0 deficit in the decider, to triumph 5-7 6-2 7-6(4).

"My coach nicknamed me 'Showtime' when I was young because I always love to play in front of people. There's always a lot going on but it keeps it fun," Sock told the crowd. "I don't even know what I'm doing sometimes!"

After failing to win a set in his opening round-robin loss to Roger Federer, it was imperative for Sock to beat Cilic, who was himself seeking a first win after a three-set defeat to Alexander Zverev on Sunday.

With Federer tipped to steamroll Group Boris Becker, the mini-battle between Sock, Cilic and Zverev could decide second spot – and it was the 25-year-old debutant who took a giant stride towards the semi-final with a courageous display.

The key moment came in the decisive tie-break with Cilic a mini-break ahead at 4-3.

The Croatian swatted a forehand against the net cord, sending the ball spiralling onto Sock’s side of the court for a seemingly certain winner.

But Sock somehow raced to the dying ball and clipped it back into the open court to draw level, before seizing the momentum to win the next three points and the match.

"Marin's an incredible player but I'm fortunate to get through this one and keep my hopes alive for this week," said Sock, who won his first Masters triumph in Paris to sneak into the finals.

Federer and Zverev meet later on Tuesday.