| 12 ago 2026 | Stickler, Florentin 2278 | Koellner, Ruben Gideon 2531 | ½-½ | C78 Apertura Española (Ruy López): Morphy Defense, Møller Variation | Oberbank Challenger Open 2026 | 49 | Ver |
| 12 ago 2026 | Koellner, Ruben Gideon 2531 | Badelka, Olga 2416 | ½-½ | B00 Defensa Pirc | Oberbank Challenger Open 2026 | 38 | Ver |
| 12 ago 2026 | Schernthaner, David 2380 | Koellner, Ruben Gideon 2531 | 0-1 | C78 Apertura Española (Ruy López): Morphy Defense, Møller Variation | Oberbank Challenger Open 2026 | 35 | Ver |
| 12 ago 2026 | Koellner, Ruben Gideon 2531 | Postlmayer, Jakob 2440 | 1-0 | D02 Apertura de Peón de Dama: Symmetrical Variation | Oberbank Challenger Open 2026 | 29 | Ver |
| 12 ago 2026 | Hertneck, Gerald 2415 | Koellner, Ruben Gideon 2531 | 0-1 | C41 Defensa Philidor: Lion Variation | Oberbank Challenger Open 2026 | 75 | Ver |
| 12 ago 2026 | Koellner, Ruben Gideon 2531 | Leitgeb, Julian 2298 | ½-½ | A48 East Indian Defense | Oberbank Challenger Open 2026 | 35 | Ver |
| 12 ago 2026 | Steinhauer, Artur 2187 | Koellner, Ruben Gideon 2531 | 0-1 | C70 Apertura Española (Ruy López): Morphy Defense, Classical Defense Deferred | Oberbank Challenger Open 2026 | 57 | Ver |
| 12 ago 2026 | Koellner, Ruben Gideon 2531 | Wunder, Niklas 2122 | 1-0 | A45 Ataque Trompowsky | Oberbank Challenger Open 2026 | 35 | Ver |
| 12 ago 2026 | Vincenzi, Marco 2017 | Koellner, Ruben Gideon 2531 | 0-1 | C41 Defensa Philidor: Lion Variation | Oberbank Challenger Open 2026 | 57 | Ver |
| 9 ago 2026 | Koellner, Ruben Gideon 2531 | Werthebach, Felix 2202 | 1-0 | A45 Ataque Trompowsky: Poisoned Pawn Variation | 16. Nordhäuser Open | 70 | Ver |
| 7 ago 2026 | Huber, Benedikt 2292 | Koellner, Ruben Gideon 2531 | ½-½ | B00 Defensa Pirc | 16. Nordhäuser Open | 54 | Ver |
| 7 ago 2026 | Koellner, Ruben Gideon 2531 | Ahmed, Daniel 2111 | 1-0 | D04 Apertura de Peón de Dama: Colle System | 16. Nordhäuser Open | 44 | Ver |
| 6 ago 2026 | Klein, Timon 2012 | Koellner, Ruben Gideon 2531 | 0-1 | A15 Apertura Inglesa: Anglo-Indian Defense, King's Knight Variation | 16. Nordhäuser Open | 65 | Ver |
| 2 ago 2026 | Koellner, Ruben Gideon 2531 | Peng, Li Min 2553 | 0-1 | D02 Apertura de Peón de Dama: Symmetrical Variation | 16. Nordhäuser Open | 72 | Ver |
| 26 abr 2026 | Schaefer, Markus 2362 | Koellner, Ruben Gideon 2506 | 0-1 | C41 Defensa Philidor: Lion Variation | German Bundesliga 2025/26 | 42 | Ver |
| 25 abr 2026 | Koellner, Ruben Gideon 2506 | Levin, Felix 2414 | ½-½ | D04 Apertura de Peón de Dama: Colle System | German Bundesliga 2025/26 | 88 | Ver |
| 24 abr 2026 | Koellner, Ruben Gideon 2506 | Kjartansson, Gudmundur 2407 | 1-0 | A48 East Indian Defense | BL 2526 Schachfreunde Deizisau - MSA Zugzwang | 31 | Ver |
| 6 abr 2026 | Koellner, Ruben Gideon 2506 | Abdurakhmonov, Mukhammadali 2362 | 1-0 | D04 Apertura de Peón de Dama: Colle System, Anti-Colle | Grenke Chess Festival 2026 Open | 23 | Ver |
| 6 abr 2026 | Karthik Venkataraman 2594 | Koellner, Ruben Gideon 2506 | ½-½ | C78 Apertura Española (Ruy López): Morphy Defense, Møller Variation | Grenke Chess Festival 2026 Open | 25 | Ver |
| 5 abr 2026 | Kalogridis, Antonios 2386 | Koellner, Ruben Gideon 2506 | 0-1 | A46 Defensa India: Wade-Tartakower Defense | Grenke Chess Festival 2026 Open | 64 | Ver |