Brisbane - Serena Williams credited a more subdued lifestyle on Tuesday for the current form which has put her on track to succeed fellow-American Chris Evert as the oldest No 1 in women's tennis.
Williams, who recorded a serve of 200km/h during a second-round 6-2, 6-2 win over France's Alize Cornet at the Brisbane International, is currently ranked third in the world.
However, the 31-year-old is regarded as the pre-eminent woman player at the moment after winning the Wimbledon, US and Olympic titles last year. Evert was aged 30 years 11 months when she was No 1 in 1985.
"I'm really boring now," Williams told reporters. "I used to be fun.
"For a fun time, call Serena. Now for a fun time, do not call me. I don't know what happened to me.
"I think I just got older and I realised I can't be that fun girl for the rest of my life. I think that's pretty much what it is. I could be the oldest number one. I don't know how that goes with the funnest."
Williams said she had not celebrated New Year's eve.
"I've been having insomnia," she said. "I don't know what time zone I'm in. I don't know if I'm in Florida or if I'm in Mauritius or if I'm in Brazil.
"I just don't know anymore. My body is like telling me, 'Don't sleep ever'. I'm nocturnal right now. I can't sleep at night. I was awake for New Year's eve. I heard all the fire crackers and I would have loved to have seen it but I had a match today so I didn't do anything fun."
World No 2 Maria Sharapova's preparations for the Australian Open starting in two weeks' time were interrupted by the collarbone injury which led to her pulling out of an exhibition match against Caroline Wozniacki at the end of last year.
Sharapova withdrew from her second-round match against Australian Jarmila Gajdosova and said she had been just practising ground strokes because of the injury.
"I still have quite a bit of time to prepare for the Australian Open," she said. "I'm on the right track, been training really well, so I just don't want to jeopardise what I've gained in the off-season so far."
In other matches, world number six Sara Errani was defeated 4-6, 6-1, 7-5 by Slovakia's Daniela Hantuchova while No 8 Petra Kvitovia was beaten 6-4, 7-5 by Russia's Anastasia Pavlyuchenkova.