| Apr 2, 2026 | Sieber | 0–1 | Horvath | Grenke Chess Festival 2026 Open | King's Indian Defense: Orthodox Variation | |
| Jan 5, 2026 | Scheffner | 1–0 | Sieber | Runde 7: Scheffner, Jarno - Sieber, Bert | Sicilian Defense: Kan Variation, Polugaevsky Variation | |
| Jan 4, 2026 | Sieber | 1–0 | Kieselbach | Runde 6: Sieber, Bert - Kieselbach, Marvin | Nimzo-Indian Defense: Normal Variation | |
| Jan 4, 2026 | Riemay | 1–0 | Sieber | Runde 5: Riemay, David - Sieber, Bert | Sicilian Defense: Kan Variation, Polugaevsky Variation | |
| Jan 3, 2026 | Lau | 0–1 | Sieber | Runde 4: Lau, Theodor - Sieber, Bert | Sicilian Defense: Kan Variation, Polugaevsky Variation | |
| Jan 3, 2026 | Sieber | 0–1 | Holtwessels | Runde 3: Sieber, Bert - Holtwessels, Jan | Nimzo-Indian Defense: Normal Variation, Classical Defense | |
| Jan 2, 2026 | Hoellman | 1–0 | Sieber | Runde 2: Hoellman, Ludger - Sieber, Bert | Queen's Gambit Declined | |
| Jan 2, 2026 | Sieber | 0–1 | Hampel | Runde 1: Sieber, Bert - Hampel, Felix | King's Indian Defense: Orthodox Variation, Aronin-Taimanov Defense | |
| Oct 5, 2025 | Sieber | 1–0 | Mader | Deutsche Ländermeisterschaft 2025 | Grünfeld Defense: Russian Variation, Prins Variation | |
| Oct 4, 2025 | Guo | ½–½ | Sieber | Deutsche Ländermeisterschaft 2025 | Sicilian Defense: Kan Variation, Polugaevsky Variation | |
| Oct 3, 2025 | Sieber | 0–1 | Mester | Deutsche Ländermeisterschaft 2025 | Dutch Defense: Hopton Attack | |
| Oct 3, 2025 | Belin | 1–0 | Sieber | Deutsche Ländermeisterschaft 2025 | Sicilian Defense: Kan Variation, Polugaevsky Variation | |
| Oct 2, 2025 | Sieber | 1–0 | Vortmeier | Deutsche Ländermeisterschaft 2025 | King's Indian Defense: Normal Variation, Rare Defenses | |
| Oct 1, 2025 | Grossmann | 0–1 | Sieber | Deutsche Ländermeisterschaft 2025 | Sicilian Defense: Kan Variation, Wing Attack, Fianchetto Variation | |
| Oct 1, 2025 | Sieber | 0–1 | Semling | Deutsche Ländermeisterschaft 2025 | Nimzo-Indian Defense: St. Petersburg Variation, Fischer Variation | |
| Jun 14, 2025 | Petzold | 0–1 | Sieber | DEM U18 2025 | Sicilian Defense: Kan Variation, Wing Attack | |
| Jun 13, 2025 | Sieber | 0–1 | Mueller | DEM U18 2025 | Nimzo-Indian Defense: Normal Variation, Classical Defense | |
| Jun 12, 2025 | Stork | 1–0 | Sieber | DEM U18 2025 | Queen's Gambit Declined | |
| Jun 11, 2025 | Sieber | 1–0 | Deschler | DEM U18 2025 | Queen's Gambit Declined: Exchange Variation, Positional Variation | |
| Jun 11, 2025 | Sieber | 1–0 | Eitel | DEM U18 2025 | Queen's Gambit Accepted: Central Variation, Alekhine System | |
| Jun 10, 2025 | Cilo | 0–1 | Sieber | DEM U18 2025 | Queen's Gambit Declined | |
| Jun 9, 2025 | Lippitz | 1–0 | Sieber | DEM U18 2025 | English Opening: Anglo-Indian Defense, King's Knight Variation | |
| Jun 8, 2025 | Sieber | 0–1 | Rempe | DEM U18 2025 | Nimzo-Indian Defense: Rubinstein System | |
| Jun 8, 2025 | Strehse | 1–0 | Sieber | DEM U18 2025 | Queen's Gambit Declined: Queen's Knight Variation | |
| May 25, 2025 | Sieber | ½–½ | Greiving | Round 5: Sieber, Bert - Greiving, Felix | Slav Defense: Modern Line | |
| May 24, 2025 | Daemmig | 1–0 | Sieber | Round 3: Daemmig, Matthias, Dr. - Sieber, Bert | Richter-Veresov Attack | |
| May 24, 2025 | Sieber | 1–0 | Mimkes | Round 2: Sieber, Bert - Mimkes, Antal | Queen's Indian Accelerated | |
| May 23, 2025 | Kroeze | 1–0 | Sieber | Round 1: Kroeze, Frank - Sieber, Bert | Sicilian Defense: Old Sicilian | |
| Apr 17, 2025 | Beckmann | 0–1 | Sieber | Runde 8: Beckmann, Jonathan - Sieber, Bert | Sicilian Defense: Accelerated Dragon, Maróczy Bind, Gurgenidze Variation | |
| Apr 16, 2025 | Sieber | 1–0 | Wilmink | Runde 7: Sieber, Bert - Wilmink, Anna | Queen's Gambit Declined: Austrian Defense | |
| Apr 16, 2025 | Sieber | 1–0 | Freise | Runde 6: Sieber, Bert - Freise, Linus | Nimzo-Indian Defense: St. Petersburg Variation | |
| Apr 15, 2025 | Kieselbach | ½–½ | Sieber | Runde 5: Kieselbach, Marvin - Sieber, Bert | Sicilian Defense: Accelerated Dragon, Modern Variation | |
| Apr 13, 2025 | Sieber | 1–0 | Burnus | Runde 2: Sieber, Bert - Burnus, Finn Crispin | Queen's Gambit Declined: Exchange Variation, Positional Variation | |
| Apr 12, 2025 | Ivan Jovic | 0–1 | Sieber | Runde 1: Ivan Jovic - Sieber, Bert | Queen's Gambit Declined: Queen's Knight Variation | |
| Apr 11, 2025 | Sieber | 1–0 | Ponyrko | Runde 9: Sieber, Bert - Ponyrko, Matviy | Nimzo-Indian Defense: Normal Variation | |
| Apr 11, 2025 | Sieber | 0–1 | Kieselbach | Runde 4: Sieber, Bert - Kieselbach, Jannik | Nimzo-Indian Defense: Normal Variation, Classical Defense | |
| Apr 11, 2025 | Zweigait | 0–1 | Sieber | Runde 3: Zweigait, Leon - Sieber, Bert | Sicilian Defense: Accelerated Dragon, Modern Bc4 Variation | |
| Nov 23, 2024 | Mog | ½–½ | Sieber | Round 3: Mog, Martin - Sieber, Bert | Queen's Gambit Declined: Exchange Variation, Positional Variation | |
| — | Sieber | 1–0 | Reichmann | Round 7: Sieber, Bert - Reichmann, Felix | Grünfeld Defense: Russian Variation, Byrne Variation | |
| — | Sieber | 1–0 | Schubert | Round 2: Sieber, Bert - Schubert, Matthias | Queen's Gambit Declined: Exchange Variation, Positional Variation | |
| — | Sieber | 1–0 | Huseynov | Round 4: Sieber, Bert - Huseynov, Ahad | Nimzo-Indian Defense: Rubinstein System | |
| — | Sieber | 0–1 | Steffens | Round 6: Sieber, Bert - Steffens, Olaf | English Defense | |
| — | Huber | 0–1 | Sieber | Round 6: Huber, Benedikt - Sieber, Bert | Queen's Pawn Game: Colle System | |
| — | Buergener | 0–1 | Sieber | Round 1: Buergener, Richard - Sieber, Bert | Sicilian Defense: Alapin Variation | |
| — | Krueger | 0–1 | Sieber | Round 3: Krueger, Moritz - Sieber, Bert | Catalan Opening: Open Defense, Classical Line | |
| — | Schulz | ½–½ | Sieber | Round 5: Schulz, Jannis - Sieber, Bert | Queen's Pawn Game: Accelerated London System | |
| — | Torosyan | 0–1 | Sieber | Round 7: Torosyan, Bagrat - Sieber, Bert | Sicilian Defense: Kan Variation, Polugaevsky Variation | |