Petra Kvitova's quarter-final defeat at the US Open was tinged with pride as the Czech proved her grand-slam credentials remain strong.

Kvitova, seeded 13th at Flushing Meadows, went down 6-3 3-6 7-6 (7-2) to Venus Williams (9) on Tuesday in an epic contest on Arthur Ashe Stadium.

The 27-year-old was happy to match her best run at the tournament, however, having made a near-seamless return to action after a knife attack late last year left her with severe left hand injuries.

After second-round exits at the French Open and Wimbledon this year, Kvitova saw off third seed Garbine Muguruza in New York to reach the last eight and is delighted at the prospect of returning to her previous stellar level.

"Of course, I didn't know how my career would continue," Kvitova said. "I'm glad that I am still able to compete on the high level against the top players which I hope will give me some confidence for hard work again to continue to play well, to know that it's still there somewhere.

"I'm not sure about the titles at the grand slams. Of course, that's why I'm playing tennis, and that's why I wanted to be back and playing, and is a big motivation. 

"But I'm still on the earth, and I know it's still a lot of work - even [to reach a] quarter-final, but I know how tough it is to get a title for a grand slam. It was pretty close but pretty far, as well.

"It's tough to say right now, but overall, I think [the comeback] is amazing. I didn't really think that I could come so far. 

"It was great to win in Birmingham, but I think it was pretty early that I put a little bit of pressure on me, and I just wanted to play better and better, which I wasn't pretty ready for that.

"I'm just glad that I could show it here, that there is a way to play well again. So from my side, in a couple of days I hope that I will say 'good job'. But not just now."

Kvitova hailed her conqueror Williams, saying she cannot envisage her career enjoying the same longevity that sees the 37-year-old remain a grand-slam competitor.

"Playing well in this age, after so many years, it's amazing," Kvitova added. 

"I cannot imagine myself playing at 37, but she likes it and she has the motivation. I think it's a great thing to have for her, and I just wish her luck in the end of the career, and I think that she can have so many titles still."