Dumped by her coach and struggling mentally, American tennis star CoCo Vandeweghe was "in shambles" three months ago before she started working with Australian coach Pat Cash.

Whether it was the Aussie's calming influence, steadying advice or "Jedi mind tricks" from Star Wars, the 1987 Wimbledon champion has made Vandeweghe focused and a force to be reckoned with at the US Open.

The US 20th seed dispatched world number one Karolina Pliskova of the Czech Republic 7-6 (7/4), 6-3 Wednesday to book a Thursday semi-final against either US 15th seed Madison Keys or 418th-ranked Estonian qualifier Kaia Kanepi.

After the victory, she went to the player's box and stretched up to high-five Cash.

"I think the biggest thing is channeling my intensity and tenacity out onto the court and putting it into a singular focus. I think that's probably one of the biggest things he's implemented into my regimen," Vandeweghe said.

Told how much calmer she looks on the court in a match, she said, "You will have to ask him how he's been able to do that. I don't really know. Maybe it's like some Jedi mind trick."

He's no Luke Skywalker, but he did win a Slam title, reach two Australian Open finals and the 1984 US Open semi-finals. His new pupil might even go beyond him.

Vandeweghe said she didn't "have any compelling comeback stories" like Sloane Stephens battling back after 11 months off with a left foot injury to face Venus Williams in the other smei-final.

But she did have the tale of being dropped by coach Craig Kardon after a first-round French Open exit.

"My coach at the time, Craig, he decided to end our relationship. I still had doubles and mixed to play, so I was a little bit in shambles about that," Vandeweghe said.

"Once I was done with the tournament, I went home to California for some much-needed TLC (tender love and care).

"I had a call from my agent, like, 'Hey, you kind of need a coach. You just can't go rogue out here,' which I was more on the rogue side of things than I was on, 'Let's have a coach and get this together.'"

Cash was among her options, they connected by phone and met in the Netherlands.

"The rest is what it is," Vandeweghe said.

Having reached her first Slam semi-final at the Australian Open in January, Vandeweghe followed with a Wimbledon quarter-final run and a US Open tuneup title at Stanford as well as extra work on the mental side.

"I just started it after Wimbledon when I was really disappointed on how I went out and played in my quarter-final," she said. "I was very overwhelmed by the moment and I wasn't able to get myself together in order to play correctly."

Now she finds herself bettwe able to adapt in matches and dismiss frustrations.

"It's tennis -- it's not going to be smooth sailing the whole time," she said.

- Aussies loved her fire -

Vandeweghe has fed off support from the New York crowds, a spectator connection she said began with experiences in Australia.

"I think that starts from Australia. The Australian crowd was one of the first crowds that really kind of enjoyed my tennis and my personality," she said.

"They really enjoyed my fight out there on the court, like Aussies do. They love to see passion and fight and fire. I definitely bring that out onto the tennis court.

"So when I started to play some Fed Cup matches, the crowd got behind me there. The more you get used to it, the better I think you get at channeling what you want the crowd to do for you, whether it's to pump you up, to calm you down.

"I think definitely the New York crowd has stepped up in that fashion for me and really given a big positive push to my tennis this week."

Source: AFP