It came from an unexpected source, but at last Serena Williams got what she enjoys most on the tennis court - a slugfest.

Across the net in the third round of the Australian Open Indian teenager Sania Mirza - nominally another routine victim.

In the first set it seemed a nervous Mirza was going to trudge from centre court in embarrassment.

Williams, the tournament's No.7 seed, swept past Mirza 6-1 - but then she ran into legitimate opposition as the Indian left behind her nerves and did her best to match the American's fearsome power.

While Williams wrapped up the second set and the match 6-4, she was left impressed by the rising young star.

"I was happy with the match today because in the second set - I was getting girls who weren't giving me any pace - but today she was giving me lots of hard balls," Williams said.

"She definitely got up her game and maybe I made a few errors, but I served well today after what seems like forever." Before her customary theatrical series of bows to the audience, Williams gave Mirza some words of encouragement. "It was good to see someone from India for the first time do so well - and I told her to keep fighting," she said.

"I think she had a very solid game, she's so young, she's only 18 and I see a very bright future for her." Mirza was a wildcard entry into the Australian Open when ranked 197 in the world, which represented an enormous leap from a year or so ago when she was languishing in the mid 400s.

And she promises to be the best player her country has produced.

Already she is the first Indian ever to have won both a WTA title and a junior grand slam crown.

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