MELBOURNE (AFP) - Serena Williams on Friday warned that she is playing better now than when she won three Grand Slams last year as Angelique Kerber attempts to halt the American juggernaut's record-equalling attempt in the Australian Open final.

The world No. 1 was in a different class in 2015 as she swept to the Australian Open, French Open and Wimbledon titles, losing just three matches out of 56 all season.

Despite being virtually untouchable, the 34-year-old believes her game is now on another level, with a near flawless first set against Agnieszka Radwanska in the semi-finals ample evidence.

Williams hit 18 aces to just four unforced errors in the 6-0 slaughter that the fourth-seeded Pole, who won only seven points in the set, declared was the best tennis she had ever faced.

"I would say this is probably the best Slam I've played in a year, and I've won a lot in a year," said Williams, the top seed. "Again, I haven't won this one. But even if I don't win, I really can take away that I've been really consistent, and I want to continue that."

Williams dropped sets en route to all her Grand Slam titles in 2015 but she is yet to do so at Melbourne Park ahead of her 26th Grand Slam final on Saturday.

She is attempting to equal Steffi Graf's Open-era record of 22 Slam triumphs, having snared her first Grand Slam title half-a-lifetime ago in 1999, and said she can still get better.

"I definitely can play more consistent and be more mentally stable," she said on how her game could be improved still further.