Sharapova first gained the number one ranking in LA four years ago
Maria Sharapova overcame some problems with her serve to beat eighth seed Urszula Radwanska and reach the semi-finals of the LA Championships.
The Russian, unseeded as she makes her way back after shoulder surgery, won 6-4 7-5 and next faces Flavia Pennetta, who beat second seed Vera Zvonareva.
Australian Samantha Stosur and Sorana Cirstea of Romania won their quarter-finals in the other half of the draw.
"I made a lot more errors than I wanted to," said Sharapova.
"In the second set, just kind of went off. I created so many bad habits. Eventually it's going to work itself into place."
Sharapova, currently ranked 61st, held serve just twice in the second set.
"After playing four matches, it's kind of a shock to the system," she said. "The benefit is you get in these situations and you learn from that.
"Slowly but surely I'm finding my way on the court. I feel like I'm moving better. A lot of what you lose is hand-eye coordination and I feel like I'm getting that back."
Stosur's excellent form continued as she defeated 14th seed Zheng Jie - the conqueror of world number one Dinara Safina on Thursday - 4-6 6-3 6-4.
The Australian reached a career-best ranking of 18th in June after making the last four at the French Open and is enjoying being considered more than a doubles specialist.
"It's definitely a goal of mine to try and win a singles title," she said. "I've been in four finals and lost every one of them in three sets.
"My whole career I've been trying to become a better singles player. This year it's all just come together."
Cirstea defeated Agnieszka Radwanska 7-6 (7-4) 1-6 7-5, to complete a bad day for the Radwanska family, while 10th seed Pennetta saw off Zvonareva 6-4 6-2.