LIFE on court is rarely straightforward for Serena Williams.

You get the feeling that if she ever found the powers of concentration to match her physical prowess, she would wipe the floor with every opponent in a trice. As it is, on her current form she is still good enough to get the better of everyone else: she just has to take her time getting there.

Her 3-6, 6-2, 6-3 quarter-final victory against Victoria Azarenka was a case in point. The Belarussian, whose ranking is at its lowest for nearly a decade as a result of a long absence last year with a foot injury, threw everything she had into the match on Centre Court, and appeared to catch the American off guard with the high tempo at which she began the contest. But after that sluggish start, Williams steadily ground through the gears, winning in a little over two hours.

The third set was closer on the scoresheet than the second, but in fact was quarter of an hour quicker as the five-time champion rammed home her domination. Her reward for the win is a semi-final against Maria Sharapova, who at one time was shaping up to be the biggest sustained threat to Serena and her elder sister Venus, but can currently boast only two wins out of the 19 meetings she has had with Williams the younger.

Azarenka, like Kevin Anderson against Novak Djokovic in the men's quarter-finals, had banked on being able to maintain her momentum after that sparkling start. Like Anderson, she was wrong, although as she pointed out, that had as much to do with the quality of her opponent's play as it did with her own shortcomings.

"I can't say I went out there and didn't play well," she said. "We just saw today why Serena is No. 1. I haven't seen her play like this, honestly, even the last matches before that.

"Did you see the 24 aces? That's pretty good. It's almost a set of aces. So that was a big difference.

"I think we put on a great show together really. I think it's been a while since there was that high quality of women's tennis."

If from the outside Serena's victory looked inevitable once the match had gone into a deciding set, she hinted at one of the possible causes of her victory when she explained that she actually felt less confident, not more, at that stage of a contest. "I feel really vulnerable," she said,

"I feel really vulnerable in a third set.. I just feel this is another opportunity for me to lose. I have one more set to win or to lose.

"I just go for it. At that point I kind of relax and see whatever happens happens."

There is little or no love lost between Sharapova and Serena, but the latter insisted that she enjoyed meeting the Russian. "I love playing Maria - I think she brings out the best in me. I think I bring out the best in her.

"For me, I don't feel like I have any pressure going into this match. We both actually lost early last year. We both are kind of enjoying this moment and one of us will be in the final.

The winner of the Williams-Sharapova match will meet either Agnieszka Radwanska or Garbine Muguruza in that final on Saturday. Radwanska, the runner-up to Serena three years ago, beat Madison Keys 7-6, 3-6, 6-3 in the second match on Court No 1. Muguruza, the No 20 seed from Spain, had earlier won 7-5, 6-3 on the same court against Switzerland's Timea Bacsinszky.

Having given a decent account of herself in that 2012 final against the American, Radwanska, the No 13 seed from Poland, thinks the experience will stand her in good stead if she gets through again. "Being in a final, that was a huge experience for me," she said. "I remember that match from the beginning till the end.

"I think it helps for the future, that you know how it is to be in the final of a Grand Slam. Afterwards it's a bit easier."

Keys' main weapon was her serve, Radwanska's her return, with the difference between the two being the American's unforced error count - 40 in all - and the European woman's superior composure. Radwanska can expect to face a similar barrage in Thursday's semi from Muguruza, who has beaten her in their last two meetings.

Muguruza herself, meanwhile, always had her nose in front against Bacsinszky, the No 15 seed. It was the third match in a row that the 21-year-old had beaten a more highly ranked seed, following her previous victories over Angelique Kerber and Caroline Wozniacki, the Nos 10 and 5 respectively.