Julia Goerges stunned world number one Caroline Wozniacki 7-6 (7-3) 6-3 to triumph at the Stuttgart Grand Prix.
It was Goerges's second career title and makes her the first German since Anke Huber in 1994 to win the event.
The 22-year-old, who collects a sports car and a cheque for £67,000, sent down 38 winners to Wozniacki's nine and will enter the top 30 for the first time.
"Julia played very well, very aggressive and the balls were going in," said Wozniacki.
"I tried everything but it did not work.
"I'll have to go back on the practice court and make things better. Hopefully we will have many more matches in the future."
For Wozniacki it was a second final defeat in 2011 after losing to Russia's Vera Zvonareva in Doha in February.
She was looking for her fourth title of the year - and first at this fast indoor clay court tournament - but was comprehensively outplayed.
A beaming Goerges, who won in Bad Gastein, Austria, in 2010 but had never captured a title in one of WTA's premier events, stated: "I don't quite know how I did it.
"Against Caroline it feels like you always have a mountain to climb and I did it."
Goerges pinned Wozniacki back from the start, constantly playing to the Dane's backhand and forcing her into errors.
The big-serving world number 32 did not allow her 20-year-old opponent any chance to break in the first set and a tie-break beckoned.
She opened up a 5-2 lead when Wozniacki put a crosscourt forehand into the net and grabbed the set on her second opportunity when the top seed sent another forehand long.
In the second set, the confident Goerges upped the pressure and broke Wozniacki to open up a 3-0 gap.
Wozniacki finally got her first break points at 3-1 but Goerges's forehand and a volley gave her a 4-1 lead.
Goerges missed one match point at 5-2 but had two more in the next game, clinching victory with an unreturnable serve.