Jelena Jankovic was overjoyed after becoming world number one for the first time at the end of last year, but the Serb has been frustrated by her sluggish start to 2009.
The 24-year-old has reached only one semi-final in three tournaments this season and has lost some of her explosive court speed while working to build up her stamina.
"I am not really satisfied with the way I began my year," Jankovic told reporters on Wednesday while preparing for the Indian wells WTA tournament.
"I didn't play well at the Australian Open," she added, referring to her fourth-round loss there to Marion Bartoli.
"I was completely off my game and I was moving terribly. I just didn't feel confident on the court at all and the results showed."
Jankovic, who won four WTA titles last year while reaching her first grand slam final at the US open, attributed her reduced court speed to her fitness training during the off-season.
"I did a lot of things for my endurance and I had some problems moving," she said. "I lost my speed on the court and I lost my reaction. I lost my biggest weapon.
"Until now, I was having trouble reacting and moving, especially with my returns and getting that first step. I just lost that and I have been trying to get that back.
"I hope to get my game together and start playing on a high level again. That is my goal for this moment. I am not thinking about anything else. I am not putting expectations on myself."
Jankovic, seeded second at Indian Wells, reflected with pride on her barn-storming finish to her 2008 campaign.
"I ended the year in a really good way when I had a lot of pressure on me," she said. "Everybody wanted to finish number one and I am only the ninth player to do that.
"I really wanted that number one position and I knew I had to win three tournaments in a row to secure my ranking. And I have done that.
"I proved to myself I was able to play on a high level, play under pressure and take on that role as the number one player in the world. I really liked that challenge."