Tsvetana Pironkova's inspiring U.S. Open run after three long years away from the game came to a close on Wednesday and the Bulgarian walked away from the Grand Slam with no regrets having surprised even herself.

Pironkova, who during her break gave birth to a son in April 2018, beat two seeded players en route to a quarter-final loss to Serena Williams where she took the first set off the six-times U.S. Open champion.

"I had my doubts coming to my first match, but things started to work well for me. I played well. I was feeling well. I was feeling confident," said Pironkova.

"So I did everything I can to use this opportunity to the max and to try to get the furthest that I can, and I think I did a good job with that."

This marked the fourth time Pironkova reached the quarter-finals of a Grand Slam and she called her unexpected run one of the most special moments of her career.

Pironkova, 32, knows her performance will undoubtedly ramp up others' expectations for her going forward but she does not plan to put any added pressure on herself.

"I will try not to, because I know for sure that's what helped me here is just go in the court and try to enjoy it as much and to play my best tennis carefree," she said. "Going to try to keep it that way, I hope."

Pironkova used her slice forehand to perfection to unsettle Williams early on and tried to make adjustments as the match wore on but became tired as Williams used her powerful serve in crucial moments to take control.

"I was trying different things all the time, but it's very hard to resist against a strength like that," said Pironkova. "I'm not sure how many miles an hour was her serve, but it felt like a bomb at one point."