Stadium: Court 06 Round: 44 Ground: Clay
| ITF W60 Collonge-Bellerive | 2021/08/30 09:40 | Mariia Kostiuk v Tina Nadine Smith | 1-6,2-6 |
| ITF W25 Verbier | 2021/08/22 09:10 | Matilde Paoletti v Mariia Kostiuk | 6-4,6-0 |
| ITF W25 Les Contamines | 2021/07/18 12:55 | Pauline Wuarin v Mariia Kostiuk | 6-2,6-2 |
| ITF W100 Contrexeville | 2021/07/04 09:05 | Mariia Kostiuk v Tina Nadine Smith | 0-6,0-6 |
| ITF W60 Montpellier | 2021/06/27 15:10 | Mariia Kostiuk v Camilla Rosatello | 0-6,0-6 |
| UTR Pro Tennis Series Barcelona Women | 2021/06/13 09:30 | Mariia Kostiuk v Eleanor Baglow | 1-6,2-6 |
| UTR Pro Tennis Series Barcelona Women | 2021/06/10 08:00 | Mariia Kostiuk v Romy Kolzer | 0-6,1-6 |
| UTR Pro Tennis Series Barcelona Women | 2021/06/09 12:00 | Mariia Kostiuk v Valentyna Ivakhnenko | 1-6,1-5 |