Caroline Wozniacki on Sunday admitted she found it tough trying to stay at the top after nearly a year as world number one as she prepared to defend her Pan Pacific Open title.
"It's very tough to be number one. But it's even tougher to stay there because everyone wants to beat you," she said, as the first round of the $2.05 million tournament got underway.
Wozniacki, who lost to Serena Williams in the US Open semi-finals, won the Pan Pacific title last year, which helped her reach the top ranking on October 11, 2010.
"It's always nice to be back to a tournament where you are defending the title. It's a special feeling. I am going to try to do my best to defend it."
She is among seven of the world's top 10 players - including the top four - gunning for the trophy in the star-studded tournament.
Crowd favourite Maria Sharapova, who won the title two years ago and was also champion in 2005, returned as the number-two seed after a "rewarding" season that has seen her achieve her highest ranking since she returned from shoulder surgery in 2009.
It is a sharp contrast from last year, when the Russian exited the Tokyo event in a first-round upset loss to Japanese veteran Kimiko Date Krumm.
"I had a tremendous year, back in number-two in the world. So I am quite excited about the future as well," said Sharapova, a Wimbledon finalist and semi-finalist at the French Open.
Her early elimination in the US Open earlier this month was a disappointment, but "in terms of a bigger picture, I am a lot happier" than last year, she said.
"I have been very healthy. My shoulders have been feeling really good. This time of the year, it's so important to keep that going," she said as the season nears its end.
The top two women will face a strong field of rivals, including Wimbledon winner Petra Kvitova, US Open winner Samantha Stosur, world number three Victoria Azarenka and number four Vera Zvonareva.
Before the matches began, the organisers and players held a short ceremony to recognise the devastation wrought by the 9.0-magnitude quake and tsunami in March that left more than 20,000 dead or missing along Japan's northeastern Pacific coast.
The disasters triggered a series of meltdowns and explosions at the Fukushima nuclear power plant, the world's worst nuclear crisis since Chernobyl 25 years ago that scared some top athletes and musicians from visiting Japan.
"There was definitely a lot of talk before the tournament, a lot of players having concerns whether it's safe to come here," Sharapova said.
"I know that a few actually didn't come here because they were a little bit scared," she said.
But the start of the tournament and presence of the top players should serve as "a big statement" of support for Japan in the time of crisis, Sharapova said.