| Game |
| Result | Moves |
Year |
Event/Locale | Opening |
| 1. N Huschenbeth vs M Sieciechowicz |
| 1-0 | 57 |
2007 |
17th EU-ch U16 Boys | B96 Sicilian, Najdorf |
| 2. M Sieciechowicz vs N Lorand |
| 1-0 | 55 |
2008 |
EU-ch U16 18th | D34 Queen's Gambit Declined, Tarrasch |
| 3. L Kuchynka vs M Sieciechowicz |
| 0-1 | 67 |
2008 |
EU-ch U16 18th | B96 Sicilian, Najdorf |
| 4. M Janczarski vs M Sieciechowicz |
| ½-½ | 20 |
2008 |
EU-ch U16 18th | A14 English |
| 5. M Sieciechowicz vs I Janiashvili |
| 1-0 | 47 |
2008 |
EU-ch U16 18th | D67 Queen's Gambit Declined, Orthodox Defense, Bd3 line |
| 6. S Mazur vs M Sieciechowicz |
 | 1-0 | 56 |
2008 |
EU-ch U16 18th | C05 French, Tarrasch |
| 7. M Sieciechowicz vs L Bregadze |
| 0-1 | 49 |
2008 |
EU-ch U16 18th | D38 Queen's Gambit Declined, Ragozin Variation |
| 8. M Sieciechowicz vs H Vardanian |
| ½-½ | 67 |
2008 |
EU-ch U16 18th | E15 Queen's Indian |
| 9. M Sieciechowicz vs I Smirnov |
| ½-½ | 24 |
2009 |
Cappelle la Grande | E15 Queen's Indian |
| 10. E Iturrizaga vs M Sieciechowicz |
| ½-½ | 30 |
2009 |
Cappelle la Grande | D11 Queen's Gambit Declined Slav |
| 11. S L Ivanov vs M Sieciechowicz |
| 0-1 | 50 |
2010 |
World Junior Championship | C02 French, Advance |
| 12. V Sergeev vs M Sieciechowicz |
| ½-½ | 58 |
2010 |
XXVI Governors Cup | A01 Nimzovich-Larsen Attack |
| 13. M Sieciechowicz vs B Borsos |
| ½-½ | 36 |
2010 |
European Rapid Championship | E11 Bogo-Indian Defense |
| 14. M Sieciechowicz vs G Nikolashvili |
| ½-½ | 21 |
2010 |
WYCC Open U18 | E10 Queen's Pawn Game |
| 15. M Sieciechowicz vs R Markus |
| 0-1 | 56 |
2010 |
Wroclaw Chess Festival | E94 King's Indian, Orthodox |
| 16. M Sieciechowicz vs M Matlakov |
| ½-½ | 26 |
2010 |
World Junior Championship | D85 Grunfeld |
| 17. V Talla vs M Sieciechowicz |
| ½-½ | 30 |
2010 |
XXVI Governors Cup | C01 French, Exchange |
| 18. M Sieciechowicz vs Y Drozdovskij |
 | ½-½ | 29 |
2010 |
Cappelle la Grande | D38 Queen's Gambit Declined, Ragozin Variation |
| 19. Judit Polgar vs M Sieciechowicz |
| 1-0 | 46 |
2010 |
European Rapid Championship | B90 Sicilian, Najdorf |
| 20. M Sieciechowicz vs J D Gemy |
| 1-0 | 50 |
2010 |
WYCC Open U18 | D15 Queen's Gambit Declined Slav |
| 21. M Bartel vs M Sieciechowicz |
 | 0-1 | 24 |
2010 |
Wroclaw Chess Festival | C17 French, Winawer, Advance |
| 22. M Sieciechowicz vs A Jakubiec |
| 1-0 | 40 |
2010 |
XXI Cracow Open | A80 Dutch |
| 23. O Wieczorek vs M Sieciechowicz |
| 1-0 | 53 |
2010 |
World Junior Championship | C18 French, Winawer |
| 24. M Sieciechowicz vs S P Sethuraman |
 | 1-0 | 33 |
2010 |
XXVI Governors Cup | D44 Queen's Gambit Declined Semi-Slav |
| 25. M Mchedlishvili vs M Sieciechowicz |
| 1-0 | 26 |
2010 |
European Rapid Championship | A15 English |