| Game |
| Result | Moves |
Year | Event/Locale | Opening |
| 1. N Mikkelsen vs J K Nielsen |
| 1-0 | 24 | 2002 | Politiken Cup | A45 Queen's Pawn Game |
| 2. J H Nielsen vs J K Nielsen |
| 1-0 | 26 | 2002 | Politiken Cup | B02 Alekhine's Defense |
| 3. H K Simonsen vs J K Nielsen |
| 1-0 | 25 | 2003 | Politiken Cup | E92 King's Indian |
| 4. J K Nielsen vs J W Knudsen |
| 0-1 | 22 | 2003 | Politiken Cup | B21 Sicilian, 2.f4 and 2.d4 |
| 5. H Rasmussen vs J K Nielsen |
| 1-0 | 38 | 2003 | Politiken Cup | E92 King's Indian |
| 6. J K Nielsen vs R Salomonsen |
| 0-1 | 15 | 2003 | Politiken Cup | B21 Sicilian, 2.f4 and 2.d4 |
| 7. S Jensen vs J K Nielsen |
| 1-0 | 22 | 2003 | Politiken Cup | B02 Alekhine's Defense |
| 8. J K Nielsen vs H K Edwardsson |
| 1-0 | 52 | 2003 | Politiken Cup | C33 King's Gambit Accepted |
| 9. J K Nielsen vs K V Pedersen |
| 0-1 | 10 | 2003 | Politiken Cup | B05 Alekhine's Defense, Modern |
| 10. M Kopischke vs J K Nielsen |
| 1-0 | 35 | 2003 | Politiken Cup | E90 King's Indian |
| 11. A F Kristjansson vs J K Nielsen |
| 1-0 | 22 | 2003 | Politiken Cup | B04 Alekhine's Defense, Modern |
| 12. J K Nielsen vs J N Christensen |
| 0-1 | 13 | 2004 | Copenhagen AS04 Centenary | C30 King's Gambit Declined |
| 13. J K Nielsen vs M Svendsen |
| 0-1 | 28 | 2004 | North Sea Cup | B23 Sicilian, Closed |
| 14. M Nielsen vs J K Nielsen |
| 1-0 | 31 | 2004 | North Sea Cup | B03 Alekhine's Defense |
| 15. B Skjoldan vs J K Nielsen |
| 1-0 | 32 | 2005 | Politiken Cup | E62 King's Indian, Fianchetto |
| 16. J K Nielsen vs A C Taylor |
| 0-1 | 40 | 2017 | Xtracon Chess Open | A46 Queen's Pawn Game |
| 17. J Thybo vs J K Nielsen |
| 0-1 | 27 | 2017 | Xtracon Chess Open | C36 King's Gambit Accepted, Abbazia Defense |
| 18. J K Nielsen vs M Skjoldager |
| 0-1 | 29 | 2017 | Xtracon Chess Open | C54 Giuoco Piano |
| 19. F Svane vs J K Nielsen |
| 1-0 | 16 | 2017 | Xtracon Chess Open | D93 Grunfeld, with Bf4 & e3 |
| 20. David Maselli vs J K Nielsen |
| 0-1 | 26 | 2017 | Xtracon Chess Open | D47 Queen's Gambit Declined Semi-Slav |
| 21. J K Nielsen vs J Mejvik |
| 0-1 | 18 | 2017 | Xtracon Chess Open | C34 King's Gambit Accepted |
| 22. P Fransson vs J K Nielsen |
| 1-0 | 18 | 2017 | Xtracon Chess Open | A52 Budapest Gambit |
| 23. J K Nielsen vs S Joensen |
 | 1-0 | 27 | 2017 | Xtracon Chess Open | C35 King's Gambit Accepted, Cunningham |
| 24. K Yilmaz vs J K Nielsen |
| 0-1 | 47 | 2017 | Xtracon Chess Open | B23 Sicilian, Closed |
| 25. J K Nielsen vs S Lunde |
| ½-½ | 37 | 2017 | Xtracon Chess Open | B20 Sicilian |
Kibitzing
