Head to head
0
Hard
2
0
Clay
1
1
Carpet
1
Jan Siemerink's wins on the left · Daniel Vacek's on the right · bar lengths share one scale
All meetings (5)
| 1998 | Long Island | Hard | R16 | Daniel Vacek | 6-1 4-6 6-3 |
| 1998 | Cincinnati Masters | Hard | R16 | Daniel Vacek | 6-1 6-4 |
| 1997 | Rotterdam | Carpet | R32 | Daniel Vacek | 7-6(3) 7-6(2) |
| 1995 | Hamburg Masters | Clay | R32 | Daniel Vacek | 4-1 RET |
| 1993 | Rotterdam | Carpet | R32 | Jan Siemerink | 6-4 6-7(4) 6-1 |
Methodology
Head-to-head totals and surface splits exclude walkovers (no match was played), which follows ATP convention — walkover meetings still appear in the match list. The momentum chart plots the running lead across all counted meetings, oldest to newest.