First, she's going to stick around to watch her sister's resurgence. Venus Williams raised both arms and jumped -- kicking up her heels

By JOE KAY
AP Sports Writer

MASON, Ohio (AP) -- Only one of the Williams sisters is heading to a semifinal, and it's not the one with the long winning streak. Serena Williams lost that, and her cool, at the Western & Southern Open.

Williams had her 19-match streak snapped by Germany's Angelique Kerber on Friday, a 6-4, 6-4 defeat that marked the first time she'd even lost a set since her title at Wimbledon. The third-longest winning streak of her career didn't end quietly.

She flung her racket at the ground, picked it up and slammed it on the court again as the second set slipped away.

“I probably need a break,'' she said.

While Serena fumed over missed shots, older sister Venus had another jump-for-joy day. She reached the semifinals of a tournament for the first time this season by beating Samantha Stosur 6-2, 6-7 (2), 6-4.

After all of her summer success on Wimbledon's grass, Serena Williams is having a tough time getting readjusted to hard surfaces. One of the best stretches of her career included single and doubles gold medals at the Olympics in London.

She came into Friday's match with a 64-4 record in the summer hard-court season over the last two years. Against Kerber, her game fell apart.

She missed so many easy shots that after she hit an overhead that landed in the court, she smiled and raised her arms in mock triumph.

Her sister thinks the last few weeks have caught up with her.

“She's played so many matches since Wimbledon,'' Venus Williams said, as her sister struggled on the court. “I don't think anyone has played as many matches and played as successfully as her.

“I think some rest is in order for her.''

Wearing an Olympics shirt after her match, Serena Williams agreed she needs a little time to get recharged for the U.S. Open.

“I'll be better in New York, I promise,'' she said.

First, she's going to stick around to watch her sister's resurgence. Venus Williams raised both arms and jumped -- kicking up her heels -- after winning a three-setter for the third time in the tournament, an indication she's learning to manage an immune system disorder that leaves her tired.

She'll play China's Li Na in the semifinals.

“For me and everything that's gone on in my life, it's a huge achievement and I want to take it further,'' Venus Williams said.