The 21-year-old Spaniard triumphed 6-4, 6-2 over the sixth-ranked Czech, who last year was the first unseeded woman to win the title at the All England Club.
German legend Steffi Graf was the last defending champion to lose in the opening round, when she was beaten by Lori McNeil in 1994.
Until Tuesday she had never defeated a top-40 player, while her only other grass-court match this year was a first-round loss in a low-key event in Italy.
"I think this is one of the most important moments in my life and career," said Bouzas Maneiro.
"She is one of the best players in the world so there was no pressure for me. I could just enjoy the moment and play freely."
She added: "I'm really surprised with myself. I was a little bit nervous at the start but the atmosphere was so nice that I felt more comfortable. I felt at home."
Bouzas Maneiro will face either Ana Bogdan of Romania or Spanish compatriot Cristina Bucsa for a place in the last 32.
Vondrousova had arrived in London as a fitness doubt after injuring her right hip in a fall at the Berlin grass-court tournament last month.
