Sergiy suffered a close 4-6, 5-7 defeat to no.1 seed Ricardas Berankis in quarter-final action at the 2016 Santaizi Challenger on Friday.
The Lithuanian broke once in each set and denied Stako a single break point opportunity during the one hour, 35-minute clash.
Stats: aces (14-4), double faults (0-1), 1st serve points won % (68-82), total points won (67-78).
No.5 seed Sergiy has moved into the 2016 Santaizi Challenger last eight on Thursday, after edging Jason Jung (TPE) in straight sets, 6-2, 6-3.
Stako broke twice in the first set and once in the second to advance after 58 minutes of play. He won 90% of his first service points.
Stats: aces (13-5), double points (2-2), total points won (60-41).
Sergiy previously beat Michal Przysiezny of Poland 6-7 (7), 7-5, 6-1.
The Kiev native next faces top seed Ricardas Berankis (LTU).