| UTR Pro Tennis Series Copenhagen | 2021/06/18 11:00 | Benjamin Hannestad v Nikolaj Katic | 6-4,6-1 |
| UTR Pro Tennis Series Copenhagen | 2021/06/17 08:00 | Daniel De Jonge v Nikolaj Katic | 4-6,6-4,6-0 |
| ITF Turkey F3 | 2018/01/20 09:00 | Nikolaj Katic v Roberts Grinvalds | 0-6,4-6 |
| ITF Turkey F1 | 2018/01/07 08:30 | Zizou Bergs v Nikolaj Katic | 6-2,6-1 |
| ITF Turkey F1 | 2018/01/06 09:00 | Philipp Sikorski v Nikolaj Katic | 2-6,6-1,2-6 |
| ITF Turkey F47 Qual | 2017/12/09 06:45 | Gregorio Cordonnier v Nikolaj Katic | 6-7,6-4,6-2 |
| ITF Turkey F46 Qual | 2017/12/02 06:45 | Maurizio Speziali v Nikolaj Katic | 6-1,4-6,6-1 |
| ITF Turkey F45 Qual | 2017/11/26 06:30 | Vladislav Melnic v Nikolaj Katic | 6-4,6-2 |
| UTR Pro Tennis Series Copenhagen | 2021/06/18 12:30 | Ludvig Aaes v Warren Sinius | 7-6,6-2 |
| UTR Pro Tennis Series Copenhagen | 2021/06/17 09:30 | Dominik Palan v Warren Sinius | 2-2 |
| UTR Pro Tennis Series Copenhagen | 2021/06/16 11:00 | Philip Hjorth v Warren Sinius | 6-3,6-5 |
| UTR Pro Tennis Series Copenhagen | 2021/06/14 09:30 | Marius Ruzgas v Warren Sinius | 6-2,6-0 |
| UTR Pro Tennis Series Bucharest | 2021/06/04 11:30 | Warren Sinius v Valentin Vanta | 0-6,2-6 |
| UTR Pro Tennis Series Bucharest | 2021/06/03 07:30 | Marcelo Zormann v Warren Sinius | 6-0,6-0 |
| UTR Pro Tennis Series Bucharest | 2021/06/02 12:00 | Ihor Dudun v Warren Sinius | 4-6,0-6 |
| UTR Pro Tennis Series Bucharest | 2021/05/30 13:00 | Mihai Razvan Marinescu v Warren Sinius | 6-4,6-1 |