Serena Williams and her nearest rival, Victoria Azarenka, differed in opinion and quality of performance in taking their first steps toward a much hoped-for meeting in Sunday's final at the WTA Championships on Tuesday.

Williams crushed one of the few women to have beaten her in the past 15 months as she began defense of the title with a speedily impressive win.

The world No 1 took little more than an hour to win 6-3, 6-1 against Angelique Kerber, the German who defeated her in Cincinnati last year but who this time was outplayed from the moment she dropped serve in her opening service game.

By contrast, Azarenka appeared tired and uncertain, was far from consistent, and might easily have lost the first set during her 7-6 (4), 6-2 survival against Sara Errani, the sixth seeded Italian.

The Belarussian had difficulty forcing the pace and confirmed the impression of poor health given during her disappointing performances in Beijing and Tokyo. Improvement only came after squeezing through the first set tiebreak.

Azarenka was also ambivalent about the surface. "You know I think the court is pretty rough, I would have to say," she said frankly. "It's a little bit slow.

"But that's what we have. I think you know I can't really find excuses.

"If the surface can be a little bit better, because it's tough on the body, maybe yeah - but I think it's the last year," she said, referring to the WTA Championships moving to Singapore next year.

Williams could hardly have thought more differently. "Well you know me - you cannot ask me these questions. I will say it's fast when everyone else says it's slow," she said.

For the court to be of optimum speed it should "maybe be faster than what it is," Williams half-agreed with Azarenka.

"But I like slow surfaces, you know. I like grass, so it doesn't matter for me."

Azarenka's difficulties also derived, she suggested, from having taken a break after a disappointing Asian swing and then returning to action in a tournament in which top players clash from the first match.

It was hard to make these adaptations during a match, Azarenka admitted, but she was helped a little by Errani, who appeared to sustain a calf injury in the second set and gradually lost rhythm and confidence.

However the world No 2 might need to improve if she intends to win a group that includes Chinese star Li Na, who Azarenka only narrowly beat in the final of the Australian Open at the start of the year.

Whatever the merits of the court, Williams served superbly and generated withering power off the ground, suggesting she is as far ahead of the field as she has ever been.

Petra Kvitova also did not appear to be too bothered by the court's slowness.

The 2011 champion from the Czech republic flat-hit her way to a 6-4, 6-4 win over Agnieszka Radwanska, the third-seeded former Wimbledon finalist from Poland, and now looks well placed to qualify for the semifinals from the Red Group along with Williams.

Later the star player came out with a star quote. Williams was asked if she could ever imagine a female champion coming from Turkey during her lifetime.

"Yeah, well there is a girl that is a champion from Compton," she said with an offbeat reference to her working-class origins in Los Angeles. "So anything is possible, especially from Turkey."