Sergiy failed in attempt to qualify for the main draw at the second Grand Slam event of the season, the Roland Garros, taking place in Paris from May 22 to June 5.
The Kiev native recorded victory over Brendan Klein (6-3, 6-3), but fell in the second round to Marsel Ilhan of Turkey 4-6, 4-6.
Last year, Stako reached R2 of the main draw, where he was stopped by Steve Johnson in a tight match 6-2, 3-6, 6-7, 6-7.
Sergiy is the 2016 Seoul champion! Stako recovered from a set down to beat no.5 seed Yen-Hsun Lu 4-6, 6-3, 7-6 (7) in two hours and 33 minutes on Sunday in the final of the Lecoq Seoul Open Challenger. Lu won the opening set, but the Kiev native responded with a break in the second to force a decider. The two had traded breaks twice in the third set, before Sergiy prevailed in a tie-breaker. Congratulations!!!
Stats: aces (13-3), double faults (6-6), total points won (120-116).
Sergiy is through to the Lecoq Seoul Open Challenger final after he defeated world no.180 Alexander Kuznetsov in straight sets, 6-2, 6-4 in just 56 minutes on Saturday.
The Ukrainian capitalised on five of his eight break point chances and saved three of five break points he faced.
Stats: aces (5-4), double faults (6-3), total points won (61-43).
Stako will challenge no.5 seed Yen-Hsun Lu in Sunday`s final.
Sergiy moved into the Lecoq Seoul Open Challenger last four with a 7-5, 6-2 victory over world no.228 Duckhee Lee on Friday. Stako broke once in the first set and twice in the second, having saved the only break point he faced during the 67-minute clash. The Kiev native won 100% of points on his first serve (30/30). Stats: aces (10-0), double faults (6-1), total points won (65-47).
Sergiy next plays against Alexander Kudryavtsev of Russia with whom he reached doubles quarter-finals.
Sergiy advanced to the Lecoq Seoul Open Challenger quarter-final as Michael Berrer of Germany retired during their second round clash on Wednesday with the Kiev native leading 6-1, 1-0 after 31 minutes of play.
Stako had previously defeated Marco Chiudinelli 6-4, 6-4 in round one. He will face Duckhee Lee of Korea for a place in the last four. Sergiy will also play in the doubles quarters.
He teamed with Russian Alexander Kudryavtsev to beat Korean wild card pairing of Yunseong Chung and Soon Woo Kwon 6-1, 7-6 (4), and will challenge no.3 seeds Purav Raja and Divij Sharan of India next.
Sergiy suffered a 6-2, 4-6, 2-6 defeat to no.2 seed John Millman at the Busan Open Challenger Tour Tennis on Wednesday. The match lasted one hour and 55 minutes.
Stako broke five times from 12 opportunities, while his Australian rival converted six of 14 break points. Stats: aces (2-2), double faults (6-5), total points won (89-96).
Sergiy and his doubles partner Marco Chiudinelli fell to no.2 seeds Sanchai and Sonchat Ratiwatana in a close first round encounter - 5-7, 7-5, 11-13.
Sergiy ralied to beat Ze Zhang of China 4-6, 6-2, 6-3 in one hour and 35 minutes on Tuesday to reach the second round at the Busan Open Challenger Tour Tennis. The Kiev native converted all five break point opportunities he earned and saved four of seven break points he faced.
Stats: aces (5-2), double faults (4-5), total points won (87-71). Stako goes on to face no.2 seed John Millman (AUS).