Alexander Zverev completed the last-four line-up of the ATP Finals with a 7-6 (7-5) 6-3 victory over John Isner on Friday.

The German came out on top in the key moments of two tightly contested sets to make sure he joins top seed Novak Djokovic in qualifying from Group Guga Kuerten.

Zverev will face Roger Federer in the semifinals, while Djokovic will take on Kevin Anderson.

Isner – who had lost his previous two outings in his debut appearance at the season-ending tournament – put up a brave fight but knew his slim chances of progressing were over once he failed to win the opener.

Both players dominated on serve throughout, Isner firing his way out of trouble when 15-30 down in the seventh game before wasting his big opportunity when Zverev was serving to stay in the set at 6-5 down.

The American, handed the chance to compete in London after Rafael Nadal withdrew due to injury, saw a set point disappear in a flash with an ace from Zverev, who was far more clinical when a chance came his way in the resulting tie-break.

The world number five produced a sublime half-volley from the back of the court to go 6-5 up and his opponent cracked under pressure on the next point, sending a forehand well wide.

The second set followed a similar pattern but, just as the prospect of another tie-break loomed, Zverev clinically claimed the crucial break in the eighth game.

He duly served out with ease against a now-limping Isner, securing his second win in the round-robin stage and a showdown with Federer.

STATISTICAL BREAKDOWN
Zverev [3] bt Isner [8] 7-6 (7-5) 6-3

WINNERS/UNFORCED ERRORS
Zverev - 25/10
Isner - 26/20

ACES/DOUBLE FAULTS
Zverev - 18/2
Isner - 10/1

BREAK POINTS WON
Zverev- 1/1
Isner - 0/1

FIRST SERVE PERCENTAGE
Zverev- 75
Isner - 61

PERCENTAGE OF POINTS WON ON FIRST/SECOND SERVE
Zverev - 85/56
Isner - 72/65

TOTAL POINTS
Zverev - 68
Isner - 56