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| 1st(1st leg) | RC Celta B | - | Marbella FC | 2:0 (2:0) | ||
| 2nd (2nd leg) | Marbella FC | - | RC Celta B | 4:5 (0:0, 2:0, 2:0) pso | ||
| 1st(1st leg): 20/05/2018 11:00 | 2nd (2nd leg): 27/05/2018 11:00 | Winner: RC Celta B | ||||
| 1st(1st leg) | UE Cornellà | - | Sporting Gijón B | 2:2 (1:0) | ||
| 2nd (2nd leg) | Sporting Gijón B | - | UE Cornellà | 2:0 (1:0) | ||
| 1st(1st leg): 20/05/2018 11:00 | 2nd (2nd leg): 26/05/2018 17:00 | Winner: Sporting Gijón B | ||||
| 1st(1st leg) | CF Fuenlabrada | - | Real Sociedad B | 0:0 (0:0) | ||
| 2nd (2nd leg) | Real Sociedad B | - | CF Fuenlabrada | 1:1 (0:0, 0:0) aet | ||
| 1st(1st leg): 20/05/2018 11:00 | 2nd (2nd leg): 26/05/2018 16:00 | Winner: CF Fuenlabrada | ||||
| 1st(1st leg) | Athletic Bilbao B | - | Villarreal CF B | 1:3 (0:1) | ||
| 2nd (2nd leg) | Villarreal CF B | - | Athletic Bilbao B | 0:2 (0:2) | ||
| 1st(1st leg): 20/05/2018 17:30 | 2nd (2nd leg): 26/05/2018 17:50 | Winner: Villarreal CF B | ||||
| 1st(1st leg) | Real Murcia | - | Elche CF | 0:1 (0:0) | ||
| 2nd (2nd leg) | Elche CF | - | Real Murcia | 3:2 (2:1) | ||
| 1st(1st leg): 20/05/2018 17:30 | 2nd (2nd leg): 26/05/2018 16:30 | Winner: Elche CF | ||||
| 1st(1st leg) | Extremadura UD | - | Deportivo Fabril | 2:1 (2:1) | ||
| 2nd (2nd leg) | Deportivo Fabril | - | Extremadura UD | 3:2 (2:1, 2:1) aet | ||
| 1st(1st leg): 20/05/2018 19:00 | 2nd (2nd leg): 26/05/2018 16:00 | Winner: Extremadura UD | ||||
