Melbourne: World No.2 Serena Williams on Thursday gritted out a 6-3, 6-4 second round win in a high-quality encounter against Lucie Safarova in the Australian Open tennis tournament here.

The second seeded American, eyeing her seventh title here, smashed 15 aces and 35 winners in the 86-minute clash against the Czech Republican.

The match featured a combined 59 winners and 23 aces to just 39 errors.

"The last time we played was in the final of a Grand Slam ... it wasn't easy. I'm really happy to have gotten through that," Williams was quoted as saying by the tournament's website after the match.

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"Definitely played two really tough opponents (in the first round she beat former top-10 player Belinda Bencic), but it's a great way to start the tournament."

Next up for the American is compatriot Nicole Gibbs in round three.

Earlier, third seed Agnieszka Radwanska was stunned in the second round 3-6, 2-6 by Croatia's Mirjana Lucic-Baroni.