Serena Williams struggled through to the semi-finals of the JP Morgan Chase Open in Los Angeles on Friday with a three-set victory over Meghann Shaughnessy.

Less than 24 hours after rallying for victory over Daniela Hantuchova, Williams had to dig deep again to register a 6-7 (4-7) 6-1 6-4 triumph over her fellow American.

Williams said: 'I'm definitely getting more match-tough. Winning a couple of three-setters is always good to have under your belt, especially after being a set down.'

A seven-time grand slam champion, Williams advanced to a semi-final for just the second time this year.  She missed six months due to a left knee injury and made her return last month at Cincinnati, where she also reached the last four.

The absence dumped Williams into the triple digits in the rankings and she took a wild card into this hard court event, not far from her childhood home of Compton.

Although inconsistent, she has shown that when she is on her game, there are few that can match her.

'When she was in her prime, she was probably more match fit,' Shaughnessy said. 'She hasn't played much this year, but she obviously has the skill and physical ability to get where she wants to be.'

Williams had to battle back against Shaughnessy after losing the first set. She easily won the second before the match stabilised.

The players held serve through the first seven games of the third set before Williams pounced, breaking Shaughnessy to love.

Still erratic at times, Williams gave back the break in the next game but won when Shaughnessy committed her 10th double-fault on match point.

'I'm feeling really good about it,' added Williams when asked about her return. 'I feel like I'm climbing up and it's always fun to start climbing. It's cool.'

A two-time winner of this event, the 24-year-old will now meet 16th seed Jelena Jankovic, who outlasted 10th seed Ana Ivanovic 6-4 7-6 (8-6).

In the top half of the draw, top-seeded Russian Maria Sharapova's bid for a second straight title continued as she earned a 6-2 6-4 victory over countrywoman and fifth seed Dinara Safina.

Sharapova turned around her struggles against Belgium's Kim Clijsters to capture the Acura Classic last week and followed it up against Safina, who had won their last two meetings, including a fourth-round match at the French Open in June.

Sharapova stopped the streak with her eighth consecutive straight-sets win. She moved into a semi-final meeting with third-seeded compatriot Elena Dementieva, who overcame 14 double-faults and ran off 12 of the last 14 games to dismiss American wild card Bethanie Mattek 4-6 6-1 6-1.

The world's sixth-ranked player, Dementieva is in search of her first title since Tokyo in February.

She has won just one of six meetings with Sharapova and suffered straight-sets losses in the final at Indian Wells and quarter-finals at Wimbledon.

Dementieva said: 'She's very focused; it's all about her concentration. She plays every ball like it's the last one and she doesn't give you an easy point. You have to work hard against her.

'She has a great serve with good variation.  I like to return serve, but whether I can hold my serve is the question.'