World number one Serena Williams continued her seemingly unstoppable progress towards a fourth Wimbledon title.

However she was forced to work hard to dispatch inspired Czech Petra Kvitova in their semi-final clash.

The American won 7-6 (7/5) 6-2 against the world number 62 who matched her for muscle from the start of a big-hitting contest and showed enough to suggest she will be back to challenge at the All England Club in years to come.

After barging through to the last four barely needing to break sweat, Williams was expected to steamroller an opponent for whom the Centre Court appearance was also only her fourth tour-level semi-final.

But such were the searing forehand winners flying off Kvitova’s racket early in the first set that Williams required every bit of her improved big serve to swing the match finally in her favour.

The top seed has now sent down what in the women’s game is an unprecedented 80 aces in the tournament so far and after the match she said: “I didn’t hit that many aces today but honestly I’ve never served that many aces. It’s weird and exciting. I’ve always relied on my serve to be good and strong but in the eve of my career it’s just got better.”

Aggression was always likely to be the order of the day on Centre Court but it was Kvitova who was first to show that quality as she pushed Williams back and broke in the fourth game in the match with a flashing forehand.

Pumping her fist on almost every point, Kvitova quickly endeared herself to a crowd who expected a match more along the lines of a repeat of the only previous meeting between the pair, which Williams won for the loss of only three games in Australia this year.

But Kvitova’s form was there for all to see in a series of exceptional victories at the All England Club this fortnight, including a remarkable 6-2 6-0 success over third seed Caroline Wozniacki in the last 16.

And even when Williams slammed home her advantage in the second set by seizing a double break and eventually closing out the match, there was time for Kvitova to win an extraordinary 19-stroke rally and earn the favourite’s respect.

“She’s a tough player and a big fighter,” said Williams. “It took me a while to get used to her serve but I try not to worry too much out there, it’s not the time. I think that I took my opportunities better in the second set.”

Kvitova played almost flawless tennis through the first six games to establish a 4-2 lead before Williams began to respond by raising her own aggression, bringing errors from the Kvitova forehand and fashioning a break back for 4-4.

Williams then went on to clinch the first set on a tie-break, though it took her the last of three set points to do so, booming down an unreturnable serve to eventually clinch it 7-5 and move within one set of another final place.

But to Kvitova’s great credit she refused to crumble, making Williams work hard for the two breaks that followed. That amazing 19-stroke rally enabled Kvitova to save the first break point against her before Williams moved into a 5-2 lead.

The American duly served out, though not before squandering her first two match points and then getting lucky on the third via a net-cord, and she admitted she still hopes to put plenty of improvement in place for the final against Vera Zvonareva.

Williams said: “I’m still hoping to peak in the final. I won’t know until I play but hopefully I can serve even better than I did today and be more consistent off the ground. In the final you really want to play your best.

“On paper it looks like I should win but I have played Vera several times and she is a really good player and obviously a fighter. The biggest thing for me is to stay positive and not put too much pressure on myself.”

Kvitova meanwhile has more modest immediate targets. Her unexpectedly successful fortnight looks set to move her into the world’s top 30 for the first time and she believes she can build on her All England Club run.

“It was a great match for me and it was close in the first set,” said Kvitova. “I will take a little bit of confidence and I’m happy I was in the Wimbledon semi-finals. I hope to be seeded for the US Open and I hope I can improve more.”