The 19-year-old Krueger prevailed 3-6, 6-4, 7-5 over the more experienced German.
The 35-year-old Maria was on the brink of victory when she moved into a 5-2 lead in the deciding set. With little to lose, Krueger started playing a more aggressive tennis and won five straight games, sealing the match with an ace.
“I’ve never played in such an atmosphere, because throughout the tournament and in particular in the final, I’ve had enormous support. That makes this victory even better,” Krueger said.
“I know I had a difficult task and I had to come out of my comfort zone to play a kind of tennis that I’m not used to. It’s been an incredible week. I’m leaving with so much joy and also a great confidence boost ahead of Wimbledon.”
Krueger will rise from 148 in the rankings to a career high of 108.
It was the second year of the Veneto Open, the first WTA tournament played on natural grass in Italy. The courts are made on former soccer fields.
American teen Ashlyn Krueger wins first WTA title in Italy