The No.2 seed and former world No.1, who confirmed she was suffering from "a bit of a head cold", won 6-3, 6-2 against an opponent who was competitive at stages but did not have enough in her arsenal to push Williams out of her comfort zone.

Her sister Venus overcame a tougher challenge against gritty German left-hander Angelique Kerber, who regrouped from losing the first five games of the match to push the world No.6 before suffering a leg injury that allowed Williams to close out the match, 6-3, 6-3.

The sisters will have more than tennis on their minds today, with the overnight inauguration of America's first black president, Barack Obama. While neither votes because of their Jehovah's Witness beliefs, the magnitude of the moment has not escaped them, especially Serena.

"This is an amazing moment for American history," Serena said. "[Yesterday] morning I was watching [the news] on the TV before I went out to play and I looked at my arm and I literally had chill bumps.

"I'm a big fan of African-American history and learning my roots so I can be a better person. You just look at all the things we've come through and now to have this opportunity in less than 24 hours is amazing.

"I'll probably record it. I need my rest for this tournament but it's definitely something I will look at.

"I didn't vote, because I'm a Jehovah's Witness. I try to stay politically neutral and don't get involved in worldly matters. Obviously because I am black, I would be blind if I wasn't to take interest in it or I would be lying if I said I wasn't interested in what was going on."

Serena next plays Gisela Dulko.