After Struff had beaten Lajovic and Novak edged Zverev, the German doubles team secured the win against Serbia and a spot in the ATP Cup semi-finals.
Novak faced stiff resistance before rallying to seal his second singles win in Group A.
Serbia’s and world no.1 Novak Djokovic improved his perfect singles W/L record at the ATP Cup on Friday, following a 6-7 (3), 6-2, 7-5 victory over Alexander Zverev in two hours and 33 minutes.
There were no breaks in the first set. Zverev grabbed the tie-breaker to gain advantage. Djokovic quickly regained his composure, and with a double break, he sealed the second set to level. The two exchanged breaks once in the deciding third set, before Novak made a crucial break and closed out the match on second attempt.
The hard-fought win kept defending champion Serbia alive against Germany, after Jan-Lennard Struff had put his team in-front by prevailing against Dusan Lajovic 3-6, 6-3, 6-4, earlier in the day.
Match statistics: aces (11-16), double faults (5-8), winners (29-32), unforced errors (27-45), total points won (105-90).
The tie was decided by a doubles rubber, with the winner Germany booking the last four meeting with Russia.
Novak partnered Nikola Cacic against Alexander Zverev and Jan-Lennard Struff. The Serbian duo lost the match after a thrilling battle, 6-7 (4), 7-5, 7-10.