The world No. 1 has never lost in Melbourne when she's played a semifinal or final -- going 10-0 -- with her record overall in grand slam semifinals and finals an impressive 40-7.
Further not since the 2011 U.S. Open has the 33-year-old fallen in a grand slam semifinal or final.
Those are indeed ominous numbers for her semifinal opponent and fellow American Madison Keys, who prevented an all-Williams encounter in the last four when she edged Venus Williams 6-3 4-6 6-4. Keys became the third young, surprise semifinalist at the Australian Open in three seasons, joining Eugenie Bouchard and Sloane Stephens.
But Serena Williams wasn't looking too far ahead just yet.
The 18-time grand slam winner was simply happy to advance to the semifinals, having not done so in Melbourne since capturing the title in 2010.
"It's finally good to get past the quarterfinals or the fourth round," she said. "I forgot what it's like for this place, for Melbourne, to look a little empty. Gosh, it's been so long."
She progressed over 2014 finalist Cibulkova despite continuing to struggle with a sore throat.
"I've been sick the past few days," she said. "It's just getting worse and worse. But hopefully it will start getting better.
"I heard it's a virus going around with a lot of the players. I think I caught it."
The 19-year-old Keys will attempt to go one better than Bouchard and Stephens when she takes on Serena in a maiden semifinal at a major.
Against Venus Williams, the powerful Keys wasn't without her own health issues, calling the trainer for a thigh injury in the second set.
She'll hope the injury gets better -- and fast -- since Keys won't have a day off prior to the semis.
"It still hurts," said Keys. "Definitely going to be getting some treatment on that."
Keys rallied from a break down in the final set against the seven-time grand slam champion, who was competing in her first major quarterfinal in five years.
She was helped by her opponent, who committed 38 unforced errors to go along with only 10 winners. In the third set alone, Venus Williams hit three winners and 13 unforced errors.
"This is her moment today," said Venus Williams. "I think it was pretty rare that I was able to string together three or four points without an error. That was unfortunate for me today. But next time I'll be able to play more solid.
"It's definitely been a great last like four weeks, I think," added Williams, who won a warmup event in Auckland. "A lot of match wins, a lot of momentum, just a lot of great things happening that everybody wants to happen in their career.
"I think a lot of players would have been happy with this tournament. I'm happy with progress. I'm not happy with a loss, I'll tell you that."
The other semifinal is an all-Russian affair -- Maria Sharapova challenges Ekaterina Makarova.
Wawrinka betters Nishikori
Defending men's champion Stan Wawrinka continued his fine form, brushing aside Kei Nishikori.
When they met at the U.S. Open in the quarterfinals, Nishikori upset Wawrinka in five sets before later making his first grand slam final.
But Wednesday's quarterfinal contest wasn't close, with Wawrinka prevailing 6-3 6-4 7-6 (6).
Wawrinka rallied from a 5-1 deficit in a fourth-set tiebreak in his previous match against Guillermo Garcia-Lopez -- but almost blew a 6-1 lead in the fourth-set tiebreak versus Nishikori.
The Japanese baseliner drew level at 6-6, only to then miss a drop shot into the net when he was controlling the rally.
"That one I was really happy because I was not going to get to that ball," Wawrinka told reporters.
Wawrinka closed out the match with a big serve.
Wawrinka improved to 16-4 in tiebreaks in Melbourne, including 5-0 this year.
He'll next battle world No. 1 Novak Djokovic in the pair's third meeting in Melbourne in three seasons. The previous two went to five sets.
They went five sets at the U.S. Open in 2013, too.
"We had some crazy matches in the grand slams in the past," Wawrinka said.
Djokovic, in the last match on Rod Laver Arena, had little trouble defeating big-serving Canadian Milos Raonic 7-6 (5) 6-4 6-2.
He didn't face a break point.
Two-time grand slam winner Andy Murray plays 2010 Wimbledon finalist Tomas Berdych in the first men's semifinal Thursday.
Berdych upset Rafael Nadal on Wednesday and has yet to drop a set this fortnight.