Samantha Stosur must venture to uncharted territory to continue her pursuit of a second US Open crown.

Australia’s last hope once again, the 2011 champion is through to the second week at Flushing Meadows for the first time since her title defence three years ago.

But after burying some mental demons with an impressive 7-5 2-6 6-1 three-set victory over 16th seed Sara Errani, Stosur now faces another of her Italian nemeses on Monday for a coveted quarter-final spot.

Veteran Flavia Pennetta, a US Open specialist with a semi-final and four quarter-final appearances on her CV, has more than had Stosur’s measure in all six previous meetings.

Despite spending most of her career ranked above the 33-year-old, Stosur has only ever managed to take one set from the powerful world No.26 and knows she’ll need to raise her game to stay in the tournament.

“It’s something I have never done before. I have never beaten her before. I think we have played six times,” Stosur said.

“I really need to knuckle down and be clear with what I want to do and what tactics are going to work for me and how I can continually make that happen.

“I know that playing against her, I find it very difficult. She can take some of my weapons away, which is why I find it hard.

“So, yeah, I’m going to have to be really switched on.”

Although the 22nd seed hasn’t featured in the second week of a major since last year’s French Open, Stosur has already collected two titles in 2015 and her victory over Errani has further fuelled her confidence.

Errani had beaten Stosur in their past two encounters and shattered the Queenslander in Paris three years ago in one of the most disappointing defeats of her career.

But there was no repeat of Stosur’s third-set meltdown from that infamous French Open semi-final, as she broke the higher-ranked Errani twice to power through the final set in 29 minutes.

“Any win is a good win, especially in a grand slam, but I’m really pleased with the way I was able to again gain back that control and get through that,” she said.

“I’m happy to be in the second week. Happy with the way I’m playing.

“There is always things you want to improve and get better at, but you can only do what you do on any given day.

“Sara is a tricky opponent. I lost the last two times we played. I’m pleased to get through that and see what happens in the next one.”

Stosur says having partnered Pennetta in the women’s doubles at Wimbledon last year, and also in Dubai, can’t hurt.

“There are little things you do pick up when you’ve played with somebody,” she said.

“But, I mean, we played against each other enough times and practiced together enough times to kind of know little things as well.”

Stosur is carrying Australia’s singles hopes in New York after Bernard Tomic’s campaign ended in a 6-4 6-3 6-1 loss to 12th-seeded Frenchman Richard Gasquet.