By Ian Westbrook
BBC Sport at Wimbledon
Defending champion Maria Sharapova saw off a determined Nadia Petrova 7-6 (8-6) 6-3 to reach the semi-finals.
The 55-minute first set was dominated by serve, with only one break point given away, but Sharapova finally won it with her third set point.
The momentum carried Sharapova into a 3-0 lead in the second set as Petrova failed to recapture her early form.
Although Petrova finally held her serve and held a break point at 5-3 down, Sharapova served out the match.
She will play former champion Venus Williams in Thursday's semi-finals.
Sharapova stayed rooted to the baseline for almost the entire match, with fellow Russian Petrova the only player venturing to the net, albeit rarely.
Petrova's serve was especially strong early on, with only one point conceded in each of her first four service games, but although she took Sharapova to deuce once she rarely looked like breaking the champion.
Her one chance came as Sharapova served for the match but the Russian saved the point and quickly wrapped up her 22nd consecutive win on grass to reach the last four for the second successive year.
"It is so exciting to be back in the semi-finals," Sharapova told BBC Sport.
"Finishing off matches as champion is tough and it gives me shivers in my body but it is so good to get through.
"That was a really tough match. She had such a big serve and someone like that is always going to be dangerous on grass, but I saw it through."
Sharapova has made much of her greater experience this year but admitted she got lucky when break-point down while serving for the match.
"When I was down break point I told the ball to hit the net and roll over," she joked. "That's experience."
She added: "Over the past year I've been able to bounce back from losing situations. I feel like I'm mentally tougher out there."