Italian Pennetta was due to play America's Grace Min in the first round at the WTA International clay-court event in Austria, but pulled out shortly before her match due to an ankle injury.
Min will now face qualifier Beatriz Garcia Vidagany on Tuesday instead.
Pennetta's withdrawal means the draw has opened up somewhat, and eighth seed Pliskova is one player who will look to take advantage following a 6-4 6-4 win over Barthel.
The Czech will now meet the winner of Ana Bogdan and Ajla Tomljanovic in round two.
Elsewhere, home favourite Stefanie Vogele defeated 2010 champion Julia Gorges 7-6 (7-0) 6-2.
Rounding off Monday's action, Lisa-Maria Moser won the battle of the Austrian wildcards against Yvonne Neuwirth, the 23-year-old securing a 6-2 6-4 triumph.