| 20 jun 2026 | Kostolansky, Sebastian Lukas 2427 | Bochnicka, Vladimir 2357 | ½-½ | B30 Defensa Siciliana: Nyezhmetdinov-Rossolimo Attack | Majstrovstva SR | 29 | Ver |
| 19 jun 2026 | Sahidi, Samir 2484 | Kostolansky, Sebastian Lukas 2427 | 1-0 | D52 Gambito de Dama rehusado | Majstrovstva SR | 48 | Ver |
| 19 jun 2026 | Kostolansky, Sebastian Lukas 2427 | Michalik, Peter 2540 | ½-½ | B12 Defensa Caro-Kann: Advance Variation, Tal Variation | Majstrovstva SR | 30 | Ver |
| 17 jun 2026 | Neugebauer, Martin 2483 | Kostolansky, Sebastian Lukas 2427 | 0-1 | B48 Defensa Siciliana: Taimanov Variation, Bastrikov Variation, English Attack | Majstrovstva SR | 45 | Ver |
| 17 jun 2026 | Kostolansky, Sebastian Lukas 2427 | Haring, Filip 2457 | ½-½ | B51 Defensa Siciliana: Moscow Variation | Majstrovstva SR | 34 | Ver |
| 16 jun 2026 | Gazik, Viktor 2529 | Kostolansky, Sebastian Lukas 2427 | 1-0 | B48 Defensa Siciliana: Taimanov Variation, Bastrikov Variation, English Attack | Majstrovstva SR | 45 | Ver |
| 14 jun 2026 | Kostolansky, Sebastian Lukas 2427 | Rybka, Simon 2354 | ½-½ | B52 Defensa Siciliana: Moscow Variation, Main Line | Majstrovstva SR | 66 | Ver |
| 13 jun 2026 | Ftacnik, Lubomir 2423 | Kostolansky, Sebastian Lukas 2427 | ½-½ | D43 Defensa Semieslava | Majstrovstva SR | 54 | Ver |
| 13 jun 2026 | Kostolansky, Sebastian Lukas 2427 | Druska, Juraj 2465 | ½-½ | A06 Apertura Zukertort | Majstrovstva SR | 18 | Ver |
| 2 may 2026 | Liang, Awonder 2718 | Kostolansky, Sebastian Lukas 2427 | 1-0 | A05 Apertura Zukertort | rated rapid game | 58 | Ver |
| 2 may 2026 | Varela Velazquez, Carlos Francisco 2323 | Kostolansky, Sebastian Lukas 2427 | 0-1 | B47 Defensa Siciliana: Taimanov Variation, Bastrikov Variation | rated rapid game | 50 | Ver |
| 2 may 2026 | Kostolansky, Sebastian Lukas 2427 | Oosthuizen, Michal Jacobus 2074 | 1-0 | B12 Defensa Caro-Kann: Advance Variation, Botvinnik-Carls Defense | rated rapid game | 40 | Ver |
| 2 may 2026 | Chacon Salinas, Cesar 2171 | Kostolansky, Sebastian Lukas 2427 | 1-0 | E06 Apertura Catalana: Closed | rated rapid game | 58 | Ver |
| 2 may 2026 | Kostolansky, Sebastian Lukas 2427 | Veliz, Ariel 2110 | 1-0 | A12 Apertura Réti: Anglo-Slav Variation, Capablanca Variation | rated rapid game | 39 | Ver |
| 2 may 2026 | Aryan Chopra 2637 | Kostolansky, Sebastian Lukas 2427 | 1-0 | A05 Ataque Indio de Rey | rated rapid game | 57 | Ver |
| 19 ene 2026 | Cherukuri, Nitesh 2256 | Kostolansky, Sebastian Lukas 2430 | 0-1 | B46 Defensa Siciliana: Taimanov Variation | 2026 NY Marshall Winter Invitational | IM C | 31 | Ver |
| 19 ene 2026 | Kostolansky, Sebastian Lukas 2430 | Adam, Rafael 2291 | 1-0 | C88 Apertura Española (Ruy López): Closed, Anti-Marshall | 2026 NY Marshall Winter Invitational | IM C | 25 | Ver |
| 18 ene 2026 | Peycheva, Gergana 2182 | Kostolansky, Sebastian Lukas 2430 | ½-½ | E06 Apertura Catalana: Closed | 2026 NY Marshall Winter Invitational | IM C | 29 | Ver |
| 18 ene 2026 | Kostolansky, Sebastian Lukas 2430 | Paragua, Megan Althea 2222 | 1-0 | E14 Queen's Indian Defense, with e3 | 2026 NY Marshall Winter Invitational | IM C | 28 | Ver |
| 17 ene 2026 | Bortnyk, Mykola 2421 | Kostolansky, Sebastian Lukas 2430 | ½-½ | D43 Defensa Semieslava | 2026 NY Marshall Winter Invitational | IM C | 15 | Ver |