| Mar 14, 2026 | Daniel Fridman | 1–0 | Kostov | Round 7: Daniel Fridman - Kostov, Deyan Samuil | Queen's Gambit Accepted: Mannheim Variation | |
| Jun 14, 2025 | Demchenko | 1–0 | Kostov | Round 9: Demchenko, Anton - Kostov, Deyan Samuil | Queen's Pawn Game: London System | |
| Jun 13, 2025 | Prishita Gupta | 0–1 | Kostov | Round 8: Prishita Gupta - Kostov, Deyan Samuil | Sicilian Defense: Taimanov Variation, Bastrikov Variation, English Attack | |
| Jun 12, 2025 | Kostov | 0–1 | Bernadskiy | Round 7: Kostov, Deyan Samuil - Bernadskiy, Vitaliy | Trompowsky Attack | |
| Jun 11, 2025 | Alvarez Serrano | 0–1 | Kostov | Round 6: Alvarez Serrano, Carlos - Kostov, Deyan Samuil | Queen's Gambit Accepted: Classical Defense, Main Line | |
| Jun 10, 2025 | Kostov | 1–0 | Aarav Sarbalia | Round 5: Kostov, Deyan Samuil - Aarav Sarbalia | Trompowsky Attack | |
| Jun 9, 2025 | Nandish V S | ½–½ | Kostov | Round 4: Nandish V S - Kostov, Deyan Samuil | Queen's Gambit Accepted: Furman Variation | |
| Jun 9, 2025 | Kostov | 0–1 | Safarli | Round 3: Kostov, Deyan Samuil - Safarli, Eltaj | Trompowsky Attack | |
| Jun 8, 2025 | Kostov | 1–0 | Darshan G | Round 1: Kostov, Deyan Samuil - Darshan G | Queen's Gambit Declined: Exchange Variation, Positional Variation | |
| Jun 8, 2025 | Sieber | 0–1 | Kostov | Round 2: Sieber, Fiona - Kostov, Deyan Samuil | Sicilian Defense: Taimanov Variation, Bastrikov Variation, English Attack | |
| Apr 27, 2025 | Kostov | 0–1 | Baum | Round 9: Kostov, Deyan Samuil - Baum, Jonasz | Nimzo-Indian Defense: Normal Variation, Botvinnik System | |
| Apr 26, 2025 | Kostov | ½–½ | Iermito | Round 8: Kostov, Deyan Samuil - Iermito, Sebastian Dario | Queen's Gambit Accepted: Janowski-Larsen Variation | |
| Apr 26, 2025 | Woodward | ½–½ | Kostov | Round 7: Woodward, Andy - Kostov, Deyan Samuil | Queen's Gambit Accepted: Central Variation, McDonnell Defense | |
| Apr 25, 2025 | Kostov | ½–½ | Matviishen | Round 6: Kostov, Deyan Samuil - Matviishen, Viktor | Queen's Gambit Declined: Exchange Variation, Positional Variation | |
| Apr 24, 2025 | Kostov | * | Fernandez Guillen | Round 4: Kostov, Deyan Samuil - Fernandez Guillen, Ernesto J. | ? | |
| Apr 23, 2025 | Kostov | 1–0 | Cuenca Jimenez | Round 2: Kostov, Deyan Samuil - Cuenca Jimenez, Jose Fernando | Queen's Gambit Declined: Exchange Variation, Positional Variation | |
| Apr 23, 2025 | Agmanov | ½–½ | Kostov | Round 3: Agmanov, Zhandos - Kostov, Deyan Samuil | French Defense: Advance Variation, Euwe Variation | |
| Mar 15, 2025 | Kostov | 0–1 | Ivic | Round 2: Kostov, Deyan Samuil - Ivic, Velimir | King's Indian Defense: Makogonov Variation | |
| Mar 15, 2025 | Kostov | * | Dovgaliuk | Round 4: Kostov, Deyan Samuil - Dovgaliuk, Oleksandr | ? | |
| Mar 15, 2025 | Kostov | 1–0 | Bosboom | Round 6: Kostov, Deyan Samuil - Bosboom, Manuel | King's Indian Defense: Normal Variation, Rare Defenses | |
| Mar 15, 2025 | Oranje | * | Kostov | Round 1: Oranje, Richard - Kostov, Deyan Samuil | ? | |
| Mar 15, 2025 | Oskam | * | Kostov | Round 3: Oskam, Julian - Kostov, Deyan Samuil | ? | |
| Mar 15, 2025 | Vrolijk | 0–1 | Kostov | Round 5: Vrolijk, Liam - Kostov, Deyan Samuil | Zukertort Opening | |
| Mar 15, 2025 | Dgebuadze | ½–½ | Kostov | Round 7: Dgebuadze, Alexandre - Kostov, Deyan Samuil | Queen's Gambit Accepted: Normal Variation, Traditional System | |
| Sep 6, 2024 | Kostov | 0–1 | Plenca | 13. SPLIT OPEN: ŠAHOVSKI FESTIVAL 2024 | Nimzo-Indian Defense: Normal Variation, Classical Defense | |
| Aug 11, 2024 | Rahman | ½–½ | Kostov | 13. SPLIT OPEN | Queen's Pawn Game | |
| Aug 10, 2024 | Hansen | 1–0 | Kostov | 13. SPLIT OPEN | Sicilian Defense: Taimanov Variation, Bastrikov Variation | |
| Aug 9, 2024 | Kostov | 1–0 | Priasmoro | 13. SPLIT OPEN: ŠAHOVSKI FESTIVAL 2024 | Queen's Pawn Game: Torre Attack, Grünfeld Variation, Main Line | |
| Aug 9, 2024 | Kostov | ½–½ | Volodin | 13. SPLIT OPEN | Semi-Slav Defense: Stoltz Variation | |
| Aug 7, 2024 | Nomindalai Tumurbaatar | 0–1 | Kostov | 13. SPLIT OPEN: ŠAHOVSKI FESTIVAL 2024 | Queen's Gambit Accepted: Central Variation, Rubinstein Defense | |
| Aug 4, 2024 | Kostov | 1–0 | Grgantov | 13. SPLIT OPEN: ŠAHOVSKI FESTIVAL 2024 | Nimzo-Indian Defense: Normal Variation | |
| Aug 4, 2024 | Kostov | 0–1 | Kostov | 13. SPLIT OPEN: ŠAHOVSKI FESTIVAL 2024 | Sicilian Defense: French Variation, Westerinen Attack | |
| Aug 3, 2024 | Kostov | 1–0 | Day | 13. SPLIT OPEN: ŠAHOVSKI FESTIVAL 2024 | Semi-Slav Defense: Main Line | |
| Jul 5, 2024 | Dubinski | 0–1 | Kostov | 13. SPLIT OPEN: ŠAHOVSKI FESTIVAL 2024 | Sicilian Defense: Taimanov Variation, Bastrikov Variation, English Attack | |
| Jun 23, 2024 | Fischer | 1–0 | Kostov | SUI-chT Zuerich-Geneve | Sicilian Defense: Taimanov Variation, Bastrikov Variation, English Attack | |
| Apr 1, 2024 | Kostov | ½–½ | Milov | Grenke Chess Open 2024 | Dutch Defense | |
| Apr 1, 2024 | Krstulovic | 0–1 | Kostov | Grenke Chess Open 2024 | Rubinstein Opening | |
| Mar 31, 2024 | Kostov | 1–0 | Sharma Isha | Grenke Open | Nimzo-Indian Defense: Normal Variation, Botvinnik System | |
| Mar 31, 2024 | Adamovics | 0–1 | Kostov | new tournament description | English Opening: King's English Variation, Three Knights System | |
| Mar 30, 2024 | Kostov | ½–½ | Schlosser | Grenke Chess Open 2024 | Dutch Defense | |
| Mar 30, 2024 | Noe | 1–0 | Kostov | Grenke Chess Open 2024 | Queen's Gambit Accepted: Classical Defense, Main Line | |
| Oct 21, 2023 | Kostov | 1–0 | Ronce | 2. Open Hvar | Benko Gambit | |
| Oct 20, 2023 | Wu | ½–½ | Kostov | 2. Open Hvar | Queen's Pawn Game: Accelerated London System | |
| Oct 19, 2023 | Kostov | ½–½ | Ozen | 2. Open Hvar | Semi-Slav Defense: Stoltz Variation | |
| Oct 18, 2023 | Kostov | ½–½ | Ivancic | 2. Open Hvar | Semi-Slav Defense: Stoltz Variation | |
| Oct 18, 2023 | Underwood | 0–1 | Kostov | 2. Open Hvar | English Opening: King's English Variation | |
| Oct 17, 2023 | Boric | 0–1 | Kostov | 2. Open Hvar | Queen's Gambit Accepted: Classical Defense, Main Line | |
| Oct 16, 2023 | Kostov | 0–1 | Ramaj | 2. Open Hvar | Semi-Slav Defense | |
| Oct 16, 2023 | Patel | 0–1 | Kostov | 2. Open Hvar | Queen's Gambit Accepted: Alekhine Defense | |
| Oct 15, 2023 | Kostov | 1–0 | Begic | 2. Open Hvar | Queen's Gambit Declined: Exchange Variation, Positional Variation | |
| Aug 13, 2023 | Kostov | 1–0 | Kostov | 12. Split Open 05.-13.08.2023. | Queen's Pawn Game | |
| Aug 12, 2023 | Novosel | 1–0 | Kostov | 12. Split Open 05.-13.08.2023. | Queen's Gambit Accepted: Classical Defense, Main Line | |
| Aug 11, 2023 | Kostov | ½–½ | Kopylov | 12. Split Open 05.-13.08.2023. | Grünfeld Defense: Exchange Variation, Classical Variation | |
| Aug 9, 2023 | Kurtovic | 0–1 | Kostov | 12. Split Open 05.-13.08.2023. | Sicilian Defense: Kramnik Variation | |
| Aug 8, 2023 | Kostov | 0–1 | Palac | 12. Split Open 05.-13.08.2023. | Nimzo-Indian Defense: Normal Variation, Botvinnik System | |
| Aug 7, 2023 | Rasic | 0–1 | Kostov | 12. Split Open 05.-13.08.2023. | Sicilian Defense: Mengarini Variation | |
| Aug 6, 2023 | Kostov | ½–½ | Sakic | 12. Split Open 05.-13.08.2023. | Dutch Defense | |
| Aug 8, 2021 | Kostov | ½–½ | Stoimenidis | 30th OPEN Chess International Tournament | Nimzo-Indian Defense: Normal Variation | |
| Aug 7, 2021 | Kostov | * | Kostov | 30th OPEN Chess International Tournament | ? | |
| Aug 6, 2021 | Kostov | * | Tsarsitalidis | 30th OPEN Chess International Tournament | ? | |
| Aug 5, 2021 | Theodorou | 1–0 | Kostov | 30th OPEN Chess International Tournament | King's Indian Attack | |
| Aug 4, 2021 | Kostov | * | Stefanou | 30th OPEN Chess International Tournament | ? | |
| Aug 3, 2021 | Alexakis | 1–0 | Kostov | 30th OPEN Chess International Tournament | French Defense: Burn Variation | |
| Aug 2, 2021 | Kostov | * | Paterakis | 30th OPEN Chess International Tournament | ? | |
| Aug 2, 2021 | Mastrovasilis | 1–0 | Kostov | 30th OPEN Chess International Tournament | King's Indian Attack | |
| Aug 1, 2021 | Kostov | * | Karamichos | 30th OPEN Chess International Tournament | ? | |
| Jul 16, 2021 | Debevec | * | Kostov | Paracin Open | A | ? | |
| Jul 15, 2021 | Kostov | * | Khachatryan | Paracin Open | A | ? | |
| Jul 14, 2021 | Bommini Mounika Akshaya | * | Kostov | Paracin Open | A | ? | |
| Jul 13, 2021 | Zlatkov | * | Kostov | Paracin Open | A | ? | |
| Jul 12, 2021 | Kostov | * | Veljanoski | Paracin Open | A | ? | |
| Jul 10, 2021 | Kostov | * | Ellis | Paracin Open | A | ? | |
| Jul 10, 2021 | Galiev | * | Kostov | Paracin Open | A | ? | |
| Jul 9, 2021 | Iskandarov | 1–0 | Kostov | Paracin Open | A | English Opening: King's English Variation, Two Knights Variation | |
| Jul 8, 2021 | Shoshin | ½–½ | Kostov | Serbia Chess Open | Masters | ? | |
| Jul 6, 2021 | Velikic | * | Kostov | Serbia Chess Open | Masters | ? | |
| Jul 4, 2021 | Grieve | 1–0 | Kostov | Serbia Chess Open | Masters | ? | |
| Jul 3, 2021 | Kostov | ½–½ | Jordanov | Serbia Chess Open | Masters | ? | |
| Jul 3, 2021 | Zakic | ½–½ | Kostov | Serbia Chess Open | Masters | ? | |
| Jul 2, 2021 | Kostov | 0–1 | Stukan | Serbia Chess Open | Masters | ? | |