Maria Sharapova crashed to an unexpected 6-4 6-4 defeat at the hands of world number 81 Jamea Jackson in the DFS Classic semi-finals in Birmingham.
Sharapova was well short of her best form in Birmingham
Sharapova looked out of sorts early on, but both players had their serve broken with alarming regularity in the opener.
Jackson finally converted her seventh set point, and broke in the fifth game of the second set before holding on.
The 19-year-old will face Vera Zvonareva in the final after the Russian beat Meilen Tu in their semi.
Sharapova's defeat was just her fourth ever on grass, but the 2004 Wimbledon champion will clearly need to raise her game if she is to find further success at SW19.
With her normally reliable ground strokes off target, Sharapova was issued with a code violation for coaching from the sidelines from dad Yuri as she could be heard telling him to "shut up".
"I'm stunned and shocked - I don't know what to say," said Jackson.
"I am sure my mom is freaking out. She watches my games online and will have been screaming with every point. I cannot wait to call her.
"Maria's a great player who has always done well on grass, but I played well and I am so psyched to get this win.
"I've been working on my mental toughness because I've not done well after first sets, and it's really paid off in my last two games."
Sharapova shrugged off the shock defeat.
"I ran into a player who played the most unbelievable tennis of her
life," she said.
"I'll head to London and start preparing for Wimbledon.
"I just need to practice a few things and keep working hard next week and
I'll look forward to playing my favourite Grand Slam."
Zvonareva defeated friend and training partner Tu 5-7 6-4 6-3, recovering from a set behind and 4-1 down in the second set.
"It's a great feeling to be in a final again - I'm so excited," said Zvonareva.
"Tu is an unbelievable player, and I was very lucky to escape in the second set, but I think she got tired after playing six games here.
"She is a fighter, and I'm sure she will get luck on her side when she plays in the qualifiers for Wimbledon next week."