The 36-year-old Williams began Tuesday by battling past
Russia's Anastasia Pavlyuchenkova 6-4 7-6 (7-3) at Rod Laver Arena, reaching the last four Down Under for the first time in 14 years.
Federer, 35, then dismantled Mischa Zverev 6-1 7-5 6-2 in just 92 minutes, hitting 65 winners and making a mere 13 unforced errors in the process.
It is the 13th time Federer, playing his first competitive tournament since Wimbledon following a knee injury, has reached the last four in Melbourne. It also extends the Swiss' major record to 41 semifinals.
With second seed Serena Williams, 35, the favorite in the women's draw, the three thirtysomethings -- make that mid-thirtysomethings -- are thriving at Melbourne Park.
"What Roger's doing and maintaining at 35 years old, what Venus and Serena are still doing ... I know everyone talks about it," former world No. 1 Andy Roddick told reporters after being elected into tennis' Hall of Fame.
"Everyone here is going to talk about it in every story they write for the rest of this tournament, and I still don't know if that's enough. It's pretty amazing."
The 17-time grand slam winner will next face another player past the 30-mark -- though still four years younger than the four-time Melbourne champion -- in good buddy and fellow Swiss Stan Wawrinka on Thursday.
Federer said he's surprised he has gotten this far.
"Now that I'm in the semis, feeling as good as I am, playing as good as I am, that's a huge surprise to me," he told reporters. "If someone would have told me I'd play in the semis against Stan, never would I have called that one for me. For Stan, yes, but not for me.
"I honestly didn't even know a few days ago that he was in my section of the draw or I'm in his section.
"I figured it out eventually that he was playing on my days, but I never really looked in that quarter of the draw because that was just too unrealistic for me."
Federer vs. Nadal in final?
There is much talk among tennis fans about the possibility of a dream final
between old adversaries Federer and Rafael Nadal Sunday -- not to mention an all-Williams clash in the women's final Saturday.
But Federer, ranked 17th -- his lowest since 2001 -- knows defeating fourth seed Wawrinka is not a foregone conclusion, even if he does hold a commanding 18-3 record in their previous meetings. US Open champion Wawrinka downed 12th seed Jo-Wilfried Tsonga 7-6 (7-2) 6-4 6-3 earlier Tuesday.
Federer fed Zverev -- who sliced, diced and volleyed his way past world No. 1 Andy Murray on Sunday -- a double bagel 6-0 6-0 loss on grass in Halle the last time they met, in 2013.
The way he started this quarterfinal, one couldn't help but wonder if an even rarer triple bagel was in the works.
Former Wimbledon champion Goran Ivanisevic, the coach of world No. 10 Tomas Berdych, said Federer gave the Czech a "free tennis lesson" in the third round, and he was doing the same to the German in the first set, taking a commanding 5-0 lead in just 12 minutes.
Yes, this was the same Federer who did not play during the last six months of 2016.
Competing in his first grand slam quarterfinal, Zverev -- who was ranked outside the top 1,000 in 2015 as he recovered from wrist surgery -- had no time to settle.
The left-hander did offer some resistance in the second set, breaking for 3-1.
But Federer broke back and held in a key game, at 4-5, executing a gutsy second serve when 15-30 down.
The former world No. 1 broke with a passing shot in the next game to end Zverev's hopes and halt the drama which had threatened to unfold.
"He did not really let me play," Zverev told reporters.
Fiery exchange between Wawrinka & Tsonga
Federer's tussle with three-time grand slam winner Wawrinka promises to be a competitive, yet friendly, contest -- but Wawrinka's match with Tsonga was far from cordial.
The pair, always considered to be on good terms, jawed while in their chairs after Wawrinka claimed the opening set, though neither would reveal afterward what the spat was about.
"You can have some tension during the match between players," Wawrinka told reporters.
"Most important is that after the match it's all good."
Wawrinka, who won his first grand slam title in Melbourne three years ago, has more to worry about now -- overcoming the in-form Federer.
In their last grand slam duel, in the 2015 US Open semifinals, Federer pummeled Wawrinka in 90 minutes.
"I got killed in the US Open," the world No. 4 admitted. "He was playing way better than me.
"He's playing so well since the beginning of this tournament. He had some hesitation in the first two rounds, but since then he's really flying on the court.
"It's great to see him back at that level. Hopefully, I can manage to play a great match."
It looks like he'll need to if he wants to win.