Rising Ukrainian star Elina Svitolina pulled off the biggest win of her young career to knock out defending Olympic gold medalist Serena Williams in straight sets.
"The feeling is unreal, and I still can't believe this match ended with a win for me," she said after the match.
"I was trying to be focused because she's a great player with great experience coming back in many amazing matches. In the end, it was just point by point."
Johanna Konta won a marathon encounter with Svetlana Kuznetsova on Tuesday afternoon to advance to the quarterfinals of the Olympics.
After just over three hours on court a weary Kuznetsova tugged the ball wide to hand Konta a thrilling 3-6, 7-5, 7-5 victory.
"That's the longest match I've had for ages! I've been very fortunate to be part of some spectacular matches in my career and that definitely ranks up there because it's my first Olympics," Konta said.