NEW YORK, Sept ⁠7 (Reuters) - Russian fifth seed Mirra Andreeva fought back to beat Austrian Anastasia ⁠Potapova 5-7 6-4 6-3 on Monday and extend her deepest run ‌at the U.S. Open into the quarter-finals.

The 19-year-old Andreeva had her opponent on the ropes when Potapova went down with an apparent leg injury late in the match, putting a disappointing end to ​an otherwise competitive affair.

"She's my good friend and seeing ⁠what a battle we had... ⁠seeing her fall like this, it's not easy," said Andreeva. "It's not the way obviously ⁠you ‌want to finish the match... I just told her she's been playing amazing so far."

The Roland Garros winner will next play the winner of ⁠an all-American clash between IvaJovic and Coco Gauff.

Potapova put ​up less than half ‌as many unforced errors as her opponent in a tightly fought opening ⁠set, where Andreeva ​could not hang on when it counted the most, helping her opponent to the critical break in the final game with two double faults and a misfiring backhand.

But the ⁠Russian cleaned up her form considerably in the second ​set, thriving in the shorter rallies before Potapova handed over the decisive break with a double fault in the seventh game.

Andreeva broke her opponent from the baseline to ⁠go up 2-1 in the final set, where Potapova collapsed onto the court clutching her left knee in pain after chasing a ball along the baseline in the ninth game.Andreeva ran to her aid and helped her limp to her bench.

She ​lay on the court for several minutes as a ⁠physio taped up her leg and valiantly finished the match, asAndreeva clinched it with ​a backhand winner before going to the other ‌side of the court to embrace her ​opponent.

"She's a better fighter than me so I'm sure she's going to come back even stronger," said Andreeva.

(Reporting by Amy Tennery in New York)