Who will stop Serena's reign?

Serena Williams strikes an off-forehand against Andrea Petkovic in Brisbane. Source: Darren England / News Limited

SERENA Williams reapplied her headlock on women's tennis on Tuesday as one of the tour's most experienced players warned the pack pursuing her is not as strong as previous years.

World No.l Williams started her new season with the same conviction in which she dominated 2013.

Overcoming early uncertainty, she subdued German Andrea Petkovic 6-4, 6-4 in her first match of this year's Brisbane International to move into the quarter-finals.

After her 19th consecutive WTA win, stretching back to August, defending Brisbane champion Williams vowed not to burn the midnight oil on New Year's Eve.

Daniela Hantuchova, a top-five player in 2003 who is now ranked 33rd, said the chasing pack behind Williams, who last year charged through a 78-4 season, was falling further behind.

"The top 10, not that I take credit away from anyone, I think there was much more depth before,'' Hantuchova said.

"(But) the overall level of the top 100 is better. It's much harder to break through.

"If you are not ready from the first round, you are out.''

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Hantuchova was beaten by Queensland qualifier Ash Barty, ranked No.190, on Monday, which served to demonstrate her point about the increasing depth in women's tennis.

Williams, 32, and Li Na, 31, rank among the top three and the youngest among the top 10 are 23-year-olds Petra Kvitova (sixth) and Caroline Wozniacki (10).

In what now seems a vastly different era, both Maria Sharapova, in 2004, and Serena Williams, in 1999, won Grand Slam titles at 17.

When Williams won her first US Open, her victim in the final was Martina Hingis, aged 18 and the No.1.

Asked what she could hope for in 2014, Williams said: "I had a similar question in 2012. I had such a good year winning two slams and a gold and two doubles.

"I just didn't think I could do better (in 2013). You know, arguably I may have done better, so I'm just going to be up for that challenge again. Hopefully I will."'

Williams's quarter-final opponent tomorrow is Slovakian Dominika Cibulkova, a 6-3, 1-6, 6-3 winner over Japanese 43-year-old Kimiko Date-Krumm.

Williams groaned when asked she could see herself playing on the other side of 40, many years after many doubted she would be playing to the age of 30.

Kimiko Date-Krumm of Japan is still playing top-level tennis at the age of 43. Source: AFP

"I pray that I'm not playing. We'll see," she said, adding of Date-Krumm: "She's so awesome really to be out here at her age and she's probably the most fit female on tour. It's super inspiring."

World No.8 Jelena Jankovic showed no sign of making way at 28 with two straight-sets wins at Tennyson, taking down Russian Elina Svitolina 6-1, 6-3 to reach the quarter-finals.

Williams had break points against her in her first three service games of the new season, and was broken in the middle game.

But the 17-time Grand Slam title winner pounced on Petkovic's errors in the ninth for a 5-4 lead, serving the set out.

In the second set, Williams gave hackers in the capacity Rafter Arena crowd some solace by barely making contact with the ball when getting set for a short forehand putaway, which spun away from her.

"I was definitely embarrassed. I hope it doesn't make any (television) news reels," Williams said.