Stuttgart - The pink birthday cake came at the right time as Dinara Safina likes to award herself with some unhealthy food for good things she has achieved.

Turning 23 on Monday, the Russian said that "I like to give something to myself" and to "celebrate every time when the opportunity is there."

The birthday was one occasion, but Safina is also playing her first tennis tournament this week at the Porsche Grand Prix since taking the world number one ranking right days ago.

"It feels very good," she said. "Staying number one is a challenge. But I want to enjoy the challenge."

Safina was hailed as a big talent but spent a long time in the shadow of her brother Marat Safin who held the men's top spot in 2000.

Safina failed to show her full potential, falling victim to her temper and poor tactics.

The man who changed all that to the better his Zeljko Krajan, a former Croatian player who became her coach in late 2007.

"I was lucky to find the person who opened my mind. He took me from number 17 to number one," said Safina. "Before, I had the shots but didn't use them as weapons."

The breakthrough came 12 months ago in Berlin when Safina beat then number one Justin Henin and American Serena Williams en route to the title.

"Berlin changed everything," said Safina, who went on to win three more titles in 2008 and also was a finalist at the French Open and Beijing Olympics.

Safina reached another big final at the Australian Open in January but was crushed there by Williams in a match which was also for the top ranking.

She failed again at several more occasions to earn the number one, but failed again "because I got too tight and suffered in matches. It was only about winning, I wasn't as relaxed."

The top spot finally came last week and the top seeded Safina must now prove her class in Stuttgart where she could meet Serbian Jelena Jankovic, another former number one and the defending champion, in the semi-finals.

Safina does also not mind all the obligations which come with the top spot: "It will be new but this is what I wanted. I wanted to be famous."

The Porsche Grand Prix is the first official WTA clay court tournament held indoors as the buildup in Europe for the French Open starts in earnest.

Safina, who opens on Tuesday or Wednesday against Italy's Sara Errani, said she feels comfortable as she has already played several Fed Cup ties indoors on the dirt.

But she is already looking beyond Stuttgart, well aware that she will only be fully recognized as a top act with a Grand Slam title.

"My mission is nit finished yet. I want to win a Grand Slam. I have to work hard but I think I can do it. I have been in finals," Safina said. (dpa)