Van de Zandschulp led 4-3 in the first set, and Rune was serving at 40/15 when he quit due to a sore chest.
Home favourite and top seed Alexander Zverev would definitely want to forget about Wednesday as he fell to a shocking defeat against Norway's Holger Rune.
The match of the day was undoubtedly played between Alex Molcan and Norbert Gombos with the scoreline reading 6-1, 3-6, 7-6 (9-7).
The BMW Open has always had a reputation of being action-packed and looking at the entries, this season will be no exception.