'Freight train' Vandeweghe stuns Muguruza

Melbourne - Rampant Coco Vandeweghe stunned French Open champion Garbine Muguruza in a blitz of big hitting to steam into her first Australian Open semi-final on Tuesday, where she will meet fellow American Venus Williams.

The unseeded power-server upset the seventh-seeded Spaniard 6-4, 6-0 on Rod Laver Arena in a dominant display to secure her first ever berth in a Grand Slam last four.

She now faces Williams for a place in Saturday's final after the 36-year-old veteran battled past Russia's Anastasia Pavlyuchenkova in two sets.

Vandeweghe, one of the tallest women on the circuit at 1.85 metres, had been supremely confident heading into the match after stunning world number one Angelique Kerber in round three, and there was no stopping her.

"I really wasn't feeling great out there. I was nervous... I was second-guessing myself," the 25-year-old said.

"But I kept the pressure on and she finally cracked. Once I got rolling in the second set it was like a freight train, you couldn't stop it."

It is her best performance at a major, bettering her quarter-final appearance at Wimbledon in 2015, which was her only run to the last eight at a Slam until now.

The right-hander, ranked 35, has a reputation for inconsistency and she finished last season with a whimper, losing seven of her last 10 matches. But she has in brilliant form so far this year.

She has a booming serve and phenomenal groundstrokes, with a game suited to the fast and hard courts of the Australian Open.

She created two break point opportunities on the Spaniard's opening serve, but an aggressive smash and a forehand winner saved Muguruza who held to go 1-0 up.

It went with serve until a titanic seventh game that lasted 11 minutes, with the American coming out on top on her fifth break point when Muguruza sent down a double fault.

A determined Muguruza saved a set point when 3-5 down but it was staving off the inevitable as Vandeweghe thundered crisp winner after winner.

Muguruza, with her right thigh strapped, was stunned at falling behind and was unable to hit back, getting broken in the first game of the second set.

Vandeweghe was in no mood to give an inch as she blitzed through the set in just 28 minutes with Muguruza having no answers.

Known as being fiercely competitive, Vandeweghe also has a reputation for being hot-tempered.

She threw a temper tantrum in her second-round clash against Pauline Parmentier, slamming her racquet into the ground three times when she gave away a break point.

It was the second time in as many weeks that her frustrations had boiled over, pulling a similar stunt at this month's Sydney International.

But she largely kept her emotions in check against Muguruza, staying cool under pressure.

"I'm a work in progress. I'm not perfect," she said, adding that playing Williams would be "an honour".

Vandeweghe comes from a sporting family. Her mother Tauna was an Olympic swimmer and volleyballer, her grandfather Ernie played for the New York Knicks and her uncle Kiki is general manager of the Denver Nuggets.