COCO Vandeweghe accused Maria Sharapova of unsporting behaviour at the end of a tense last-eight battle which the Russian won in three sets.

The American, who lost 3-6, 7-6, 2-6 on Centre Court, implied that umpires were frightened to take the leading players to task when they appeared to contravene the rules. Sharapova now meets Serena Williams in Thursday's semi-final - the first time the two will have clashed at Wimbledon since the 2004 final.

While grunting became an issue for many television viewers on quarter-final day, with the noise coming from Sharapova and also from both players in the following match between Williams and Victoria Azarenka, Vandeweghe said she was unconcerned by any noises made by her opponent. Instead, she said that Sharapova had kept moving while waiting to receive service, and that the umpire, Eva Asderaki-Moore, did nothing about it.

"She was moving around in the middle of my motion on my second serve," the unseeded Vandeweghe said. "That's why I spoke to the umpire.

"She [the umpire] said she didn't believe she was doing it during the motion. I strongly disagreed. Towards the later end of the second set, I said if she has a problem speaking to Maria, if she's too scared to do it, I had no problem speaking to her.

"What I felt from her moving around in between my serving motion was not, I don't think, sportsmanlike, in my opinion. I try to play as fair as I can. You know, when I felt like it wasn't being reciprocated, that's when I spoke with the umpire for her to deal with."

The 23-year-old from New York contrasted the attitude of Sharapova and Asderaki-Moore with what happened at a recent tournament in 's€‘Hertogenbosch, in the Netherlands. " I was playing Tatjana Maria," she said. "The same thing was happening. I spoke to the umpire. She stopped pretty much after I spoke to the umpire."

Having made her complaint, Vandeweghe accepted that she had lost fair and square to the Russian, but expressed her delight at the form which had taken her to a Grand Slam quarter-final for the first time. "I thought off the ground, when I was receiving, she played very well. I thought it was a good battle between the two of us.

"I enjoyed my experience. I enjoyed the crowd out there. I didn't enjoy the result too much.

"It's been a long two weeks, playing singles and doubles here. I'm happy with my progress through the tournament, and I'm happy with the whole experience of it."

Vandeweghe would have been even happier if she had been able to capitalise on some early nerves from the 2004 champion at the start of a match which had been delayed by rain. Sharapova took seven minutes to hold her serve in the opening game, and only got on top in the first set after a run of three service breaks in a row put her 4-2 up.

It was the American's turn to feel the pressure at the beginning of the second set, but although she was soon a break down, she fought back at 5-4 to prevent Sharapova from serving for the match. The No 4 seed was never ahead in the tiebreak, which she lost 7-3, but her experience then told in the decider as she raced into a 3-0 lead then broke Vandeweghe a second time on her way to a victory that took her two hours 45 minutes.

"Serving for the second set, I could have made it easier for myself," Sharapova accepted. "Went into the third. I still got the job done. I have to be pleased with that - that I'm in the position of being in a semi-final again after these many years.

"As much as you want to be a perfectionist, you have to be a realist as well. If you look at Grand Slam champions, you look at their draws, matches, results - everyone comes from a few challenges, being down in matches. There's no easy road to victory. You're going to have your bumps. That's the way I see it.

"Today could have been a match in two sets. I made it more difficult for myself, but I'm still here."

Having scraped through, Sharapova opted not to make things any more difficult for herself by offering terse yet diplomatic answers when asked about Vandeweghe's allegations of gamesmanship.

Did she feel she had been doing anything differently while waiting to receive? "No, I didn't."

Did she hear her opponent complain to the umpire? "I didn't actually, no."

How would she react to the accusation of being unsporting? "It is what it is. I'm not going to argue against her words."

More generally, what would she say to people who criticised her grunting? "I don't say anything. Do I have to?"

No, she didn't. And in any case, in the next round against Williams she will have an opponent who can grunt even louder when she puts her mind to it.