| Game |
| Result | Moves |
Year | Event/Locale | Opening |
| 26. A Kostjoerin vs O Kinnmark |
| 0-1 | 18 | 1966 | Havana Olympiad qual-1 | B83 Sicilian |
| 27. A Kostjoerin vs Narino Rivera |
| 1-0 | 29 | 1966 | Havana Olympiad Final-D | C30 King's Gambit Declined |
| 28. A Kostjoerin vs A Lantsias |
 | 1-0 | 6 | 1966 | Havana Olympiad Final-D | B17 Caro-Kann, Steinitz Variation |
| 29. A Kostjoerin vs J Kozma |
| ½-½ | 105 | 1968 | Monte Carlo-B | B22 Sicilian, Alapin |
| 30. E Gereben vs A Kostjoerin |
| 1-0 | 43 | 1968 | Monte Carlo-B | A40 Queen's Pawn Game |
| 31. C Lagane vs A Kostjoerin |
| 1-0 | 24 | 1968 | Monte Carlo-B | C89 Ruy Lopez, Marshall |
| 32. P Ostojic vs A Kostjoerin |
| 1-0 | 27 | 1968 | Monte Carlo-B | B13 Caro-Kann, Exchange |
| 33. C Caminade vs A Kostjoerin |
| 1-0 | 23 | 1968 | Monte Carlo-B | B14 Caro-Kann, Panov-Botvinnik Attack |
| 34. A Casa vs A Kostjoerin |
| ½-½ | 36 | 1968 | Monte Carlo-B | C16 French, Winawer |
| 35. A Kostjoerin vs K Honfi |
| 0-1 | 31 | 1968 | Monte Carlo-B | A07 King's Indian Attack |
| 36. A Kostjoerin vs B Huguet |
| 0-1 | 39 | 1968 | Monte Carlo-B | A44 Old Benoni Defense |
| 37. A Kostjoerin vs N Minev |
| ½-½ | 26 | 1968 | Monte Carlo-B | B52 Sicilian, Canal-Sokolsky (Rossolimo) Attack |
| 38. A Kostjoerin vs S Tatai |
| 0-1 | 27 | 1968 | Monte Carlo-B | B51 Sicilian, Canal-Sokolsky (Rossolimo) Attack |
| 39. A Kostjoerin vs M Todorcevic |
| 0-1 | 29 | 1968 | Monte Carlo-B | C63 Ruy Lopez, Schliemann Defense |
| 40. R Maric vs A Kostjoerin |
| 1-0 | 22 | 1968 | Monte Carlo-B | B17 Caro-Kann, Steinitz Variation |
| 41. A Medina Garcia vs A Kostjoerin |
| 1-0 | 40 | 1968 | Monte Carlo-B | C07 French, Tarrasch |
| 42. A Kostjoerin vs D Allan |
| 0-1 | 48 | 1968 | Lugano Olympiad qual-4 | B25 Sicilian, Closed |
| 43. G McCurdy vs A Kostjoerin |
| 1-0 | 65 | 1968 | Lugano Olympiad qual-4 | C43 Petrov, Modern Attack |
| 44. F Kuijpers vs A Kostjoerin |
| 1-0 | 33 | 1968 | Lugano Olympiad qual-4 | D37 Queen's Gambit Declined |
| 45. A Dunkelblum vs A Kostjoerin |
| ½-½ | 14 | 1968 | Lugano Olympiad qual-4 | E22 Nimzo-Indian, Spielmann Variation |
| 46. A Kostjoerin vs J Santos |
| ½-½ | 31 | 1968 | Lugano Olympiad Final-C | C68 Ruy Lopez, Exchange |
| 47. A Kostjoerin vs N Dietrich |
| ½-½ | 18 | 1968 | Lugano Olympiad Final-C | B02 Alekhine's Defense |
| 48. A Kostjoerin vs A Magrin |
| 0-1 | 30 | 1968 | Lugano Olympiad Final-C | B52 Sicilian, Canal-Sokolsky (Rossolimo) Attack |
| 49. C Kulur vs A Kostjoerin |
| 1-0 | 40 | 1968 | Lugano Olympiad Final-C | E27 Nimzo-Indian, Samisch Variation |
| 50. A Kostjoerin vs J Robles |
| ½-½ | 55 | 1968 | Lugano Olympiad Final-C | B51 Sicilian, Canal-Sokolsky (Rossolimo) Attack |
Kibitzing
