Keys strikes blow to lock in semi spot

The unseeded 19-year-old overcame an injury scare to down the 18th seed in a 6-3, 4-6, 6-4 rollercoaster to set up a final four clash with the rampant top seed Serena Williams, out to avenge her sister's loss.

"The moment's definitely sweeter being able to play Venus," Keys said after defeating the 34-year-old seven-time Grand Slam winner she grew up watching in Rock Island, Illinois.

"It's amazing, obviously I was very nervous coming out but I had to embrace the moment and I did and I get to enjoy another moment in the next round."

The win is a rare moment of glory for the much-hyped new generation after rising stars such as Canadian Eugenie Bouchard and Spain's Garbine Muguruza were ousted by old stagers like Serena and Maria Sharapova.

Keys, who is coached by former Australian Open champion Lindsay Davenport, said she feared it would never happen when a thigh injury that ended her Wimbledon campaign last year flared up in the second set, forcing a lengthy medical time out.

"It was kind of an overwhelming moment. It was kind of scary," the world number 35 said, revealing she felt a moment of panic thinking the muscle could tear again.

"Luckily I was able to catch it before I did any real damage. Luckily the painkillers and adrenaline in the end kind of helped me get through it."

The injury came after Keys had won a tight first set but was trailing 4-1 in the second against a resurgent Williams.

The veteran went on to take the set and force a decider but admitted the time out disrupted her concentration, sportingly refusing to blame it for the loss.

"It's within the rules. If you don't feel well, you need an injury timeout," Williams said.

"I guess that's what happened with her. I've had them before as well. I don't really have any complaints about that rule. You have to give credit where credit is due, she played really well."

Keys, who had not been beyond the third round in 10 previous Grand Slams, said the injury forced her to go for winners to keep the points as short as possible.

"I couldn't run as much. I knew if I was going to get stretched out it was going to be more painful," she said. "It was kind of that thing if you have it, go for it, because I'm probably not going to last that long in a rally."

The third set was a see-sawing affair that went for 45 minutes, featuring four breaks of serve before Keys finally seized control and went on to win when Williams netted a return on match point.

Keys finished the match with her thigh heavily strapped but said she would not let injury fears cloud her anticipation of the semi-final against Serena on Thursday.