* Reaches quarter-finals for fourth time in New York
* Plays fellow Italian Vinci in next match (Adds quotes)
NEW YORK, Sept 2 (Reuters) - Italy's Flavia Pennetta desperately wants to make it through to the semi-finals of the U.S. Open for the first time but the prospect has left her with a heavy heart.
If she is to achieve her goal, Pennetta will have to do so at the expense of one of her closest friends, Roberta Vinci, with the pair drawn to play each other after winning their fourth round matches on Monday.
"I think it's going to be just a really tough match for both of us," Pennetta said after beating Romania's Simona Halep 6-2 7-6(3).
"We know each other really well...20 years or more, because we live almost in the same place, just 35, 45 kilometers."
Pennetta had to regain her composure after a long rain delay to reach the quarter-finals with a straight-sets win over Halep that was anything but routine.
After winning the opening set and building a 4-2 lead in the second, Pennetta suddenly lost her way as the hard-hitting Halep began to find her rhythm.
The Romanian, one of the hottest players on tour after capturing four WTA titles since June, reeled off the next three games in a row.
Then she reached set point on her own serve before play was suspended because of a thunderstorm.
The match did not resume for nearly five hours but when it did, the unseeded Pennetta burst out of the blocks quicker at Louis Armstrong Stadium.
The 31-year-old successfully saved the set point and broke Halep's serve to level the score at 5-5. And although she lost her own service game to fall behind again, she immediately broke Halep for a second time then won the tiebreaker.
"Today was a really tough match for me," said Pennetta. "It was tough to come back after so many hours.
"Waiting all day...then starting a game, it's not easy to focus."
Pennetta has never made it past the fourth round at any of the other grand slam but has flourished on the Flushing Meadows hardcourts, reaching the quarter-finals in the Big Apple in 2008, 2009, 2011 and now this year.
"Playing in New York, it's always good for me. I really love this place. I have a good memories," she said.
"This place is special for me but I can tell you the first day, when I played the first match, I didn't expect to be here today." (Reporting by Julian Linden,; editing by Gene Cherry)