LONDON (Reuters) -Unseeded Anastasia Pavlyuchenkova recovered from being robbed of a crucial point by an automated line-calling malfunction to beat Britain's Sonay Kartal 7-6(3) 6-4 to reach the Wimbledon quarter-finals on Sunday for the second time.

The Russian former French Open runner-up was left fuming after falling victim to a clear mistake when she held game point at 4-4 on serve in the opening set under the Centre Court roof.

Instead, she dropped serve to fall 5-4 behind, claiming the game had been 'stolen', but showed all of her vast experience to save a set point in the next game and break back before later going on to dominate the tiebreak with some attacking play.

Striking her heavy groundstrokes into the corners, she kept the bustling 23-year-old Kartal on the run for much of the contest and when Pavlyuchenkova won three games in a row from 2-1 down in the second set she finally began to seize control.

Kartal, the last remaining Briton in the women's singles, showed great tenacity to push her opponent hard but the Russian held her nerve at 5-4 to seal an impressive win.

"I always thought I was not good enough on grass, so this is incredible for me. Especially with me getting older, I am so impressed and proud for competing with the younger girls," Pavlyuchenkova, appearing at her 16th Wimbledon, said on court.

"My mental toughness is getting better. I used to be a little bit crazy in my head! But now I am learning to fight point by point."

She certainly showed mental resilience to put aside a moment that could have proved so costly during a tense first set which included six breaks of serve.

OPERATOR ERROR

When Kartal's shot went beyond the baseline at 4-4, Pavlyuchenkova stopped despite the automated voice calling not activating.

"STOP STOP" was heard across the court and confusion then reigned as umpire Nico Helwerth picked up his telephone for advice. Television replays showed that Pavlyuchenkova was correct and the ball had landed well out.

But instead of her being awarded the game, Helwerth said that because the technology had failed, the point must be replayed. Eventually the Russian lost the game, allowing Kartal to serve for the first set.

"Because she is local, they can say whatever. You took the game away from me. They stole the game from me. You stole the game from me," Pavlyuchenkova, was heard to say.

"Due to operator error the system was deactivated on the point in question. The chair umpire followed the established process," Wimbledon organisers said.

Fired-up by the injustice of it all, she showed true grit to raise her game and from then on was the better player, striking a total of 36 winners to Kartal's 14 as she moved through to the quarter-finals here for the first time since losing at that stage to Serena Williams in 2016.

Pavlyuchenkova will face either American 13th seed Amanda Asimova or Czech 30th seed Linda Noskova next.

Kartal, who a year ago was virtually unknown before a run to the Wimbledon third round ranked 298 in the world, can console herself with becoming the British number one after her best performance in a Grand Slam.

(Reporting by Martyn Herman, editing by Ken Ferris)