Louisa Chirico's remarkable run at the WTA Madrid Open showed no signs of losing momentum on Thursday as she eased into the semi-finals.

The American qualifier, ranked 130th in the world, defeated Monica Niculescu and Ana Ivanovic, before a walkover saw her past Victoria Azarenka and into her first Premier-level quarter-final.

And the 19-year-old showed impressive maturity against Daria Gavrilova, progressing 7-6 (7-1) 6-2 to advance to a last-four meeting with Dominika Cibulkova.

Cibulkova had to claw her way back from a set down in seeing off Sorana Cirstea 4-6 6-3 6-3, while there was a mixed display from Simona Halep.

The world number seven, runner-up two years ago, recovered admirably from a second-set bagel, overcoming fellow Romanian Irina Begu 6-3 0-6 6-1.

Halep's semi-final opponent will be Samantha Stosur, who got the better of Patricia Maria Tig 6-3 6-4.

UNCHARTERED TERRITORY FOR CHIRICO

"It's been pretty cool from the beginning really," Chirico said. "I actually wasn't in the draw. I wasn't in qualies when I landed in Madrid. I'm lucky enough to make it in and then qualify and get to where I am now. So it's been a really exciting ride so far, but I'm not finished.

"I haven't actually looked at any of the rankings or the points yet, so I usually don't do that in the tournament until afterwards. So I am just focusing on what I have to do for my next match really. All that stuff will take care of itself – afterwards I'll enjoy that."

ROMANIA RULING THE ROOST

With four Romanians in the quarter-finals, Halep believes the nation's game is in fine fettle.

"I think it's a big thing for our country," she said, before compatriots Cirstea and Tig played their matches. "It's a small country, and four girls to be in the quarter-finals of such a big tournament, it means a lot.

"I am in the semi-finals. Maybe the other two is going to be going in the semis. It's going to be a good thing."

CIBULKOVA FEELING FRESH

Each one of Cibulkova's matches has gone the distance at this tournament and Thursday's meeting with Cirstea was no different, but the Slovakian insists she is not suffering from fatigue.

"Actually, I didn't even realise I'd played all three set matches," Cibulkova said. "I said to my coach, I feel so good. I don't feel any pain or nothing. That says how physically good I'm prepared.

"Sometimes you win in two sets, sometimes it's a different story," she said. "While I'm winning, I don't care what is the score. It was another great match."