Unheralded American Collins claws into Open semis

Unheralded Danielle Collins battled from a set behind to down Russia's Anastasia Pavlyuchenkova Tuesday and take her dream debut at the Australian Open into the semi-finals.

The unseeded American beat world number 44 Pavlyuchenkova 2-6, 7-5, 6-1 in a see-sawing match to set up a final four clash with either Czech eighth seed Karolina Pliskova or 15th seeded Australian Ash Barty.

The little-known 25-year-old, who has mostly played on the US college circuit, grabbed the tennis world's attention with a 6-0, 6-2 drubbing of second seed Angelique Kerber in the fourth round.

She was unable to repeat that sizzling form against Pavlyuchenkova but finished strongly in a feisty performance as her more experienced opponent wilted under pressure.

Collins, ranked 35 in the world, who has ousted three seeds on her way to the final four, said she was relishing playing on the big stage.

"Yeah it's my first time to play on Rod Laver (Arena)," she said.

"I didn't even practice on here. It was quite the experience. I really love it." It was the fifth time Pavlyuchenkova, 27, has made a Grand Slam quarter-finals and the Russian has failed to advance every time.

Collins had never won a match at a Grand Slam in five previous attempts but is on a Cinderella run at Melbourne Park.

Pavlyuchenkova started strongly and broke in the opening game when Collins fired a forehand into the net.

The American fought desperately to get back on level terms in the next, attacking Pavlyuchenkova's second serve to carve out five break chances over 17 minutes.

But the Russian held on to make it 2-0, prompting Collins to smash her racquet to the ground in frustration.

The marathon game left her temporarily drained and Pavlyuchenkova took an easy break in the next, running away with the set after notching three breaks to one.

The American argued with the umpire over a disputed line call as Pavlyuchenkova served out the set in 49 minutes.

Collins remained vocal as she renewed her attack, yelling in triumph after securing a break in the fifth game and eventually forcing a deciding set with a cross-court forehand.

This time it was Pavlyuchenkova who was rattled, receiving a warning for time wasting as she tried to compose herself before going down a double break. Collins raced to 5-0 and left Pavlyuchenkova floundering at the net with a lob to bring up match point.

The Russian survived but it only delayed the inevitable and Collins sealed the win after two hours 16 minutes.