American Jack Sock has bounced back from a slow start to storm to a three-set upset of top seed David Ferrer and make his first ASB Classic final.

The 23-year-old Sock won 3-6 6-1 6-2 on Friday to give himself a shot of adding to his debut ATP Tour title in Houston last year.

World No.8 Ferrer, whose four Auckland crowns is the most in the Open era, was making his seventh appearance in the tournament’s semi-finals.

The 33-year-old Spaniard dominated the opening set and one break was enough for him to hit the front.

Down 2-3 and 0-40, Sock produced two big serves, including a second-serve ace, to pull two points back but his opponent responded with a pin-point forehand winner.

Things looked ominous when Sock called for a doctor after the opening set, but while he didn’t get medical treatment, he then turned the match around.

He began to find his range with his ground strokes, and aces – he went on to send down a total of 13 – started coming off his racquet with greater frequency.

Ferrer hadn’t been broken in his two previous matches this week, but dropped serve twice in both the second and third sets.

Sock will face either second-seeded Frenchman Jo-Wilfried Tsonga or Spain’s Roberto Bautista Agut, the No.8 seed, in the final on Saturday.