Williams, the 13th seed, saw off 24th seed Pavlyuchenkova 6-4 7-6 (7-3) in the first of the quarter-finals.
The 36-year-old American has never won the title, her best effort a runner-up finish to sister Serena in 2003.
She goes on to face unseeded American Coco Vandeweghe, who thrashed Spain's seventh seed Garbine Muguruza 6-4 6-0.
Vandeweghe, 25, followed up her win over world number one and defending champion Angelique Kerber with a crushing defeat of French Open champion Muguruza.
"I really wasn't feeling all that great out there, I was feeling kind of nervous," said Vandeweghe.
"I just tried to play my best, stay within myself, keep my patterns. I fought through a few break points on her serve, kept on the pressure in the first set and then she finally cracked.
"Once I got rolling in the second it was like a freight train. You couldn't stop it."
"I'd like to be champion" - Venus
Williams, meanwhile, dropped serve four times against Pavlyuchenkova but was much the stronger in the decisive moments, becoming the oldest woman to reach a Grand Slam semi-final since Martina Navratilova at Wimbledon in 1994.
"I'm so excited. Today was such a hard-fought match. She never let up," said the seven-time Grand Slam champion.
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"It's wonderful to be here at the start of the year. I want to go further. I'm not happy with this.
"I try to believe. Should I look across the net and believe the person across the net deserves it more?
"This mentality is not how champions are made. I'd like to be a champion, in particular this year. The mentality I walk on court with is: I deserve this."
On Wednesday, Serena Williams will play Britain's Johanna Konta at about 02:00 GMT, following the match between Czech fifth seed Karolina Plisokva and Croatia's Mirjana Lucic-Baroni.
|Photo by: Ben Solomon/Tennis Australia|
CoCo on the cusp
Before this week, CoCo Vandeweghe was known as a player who could occasionally take down a top player, but also as one who was extremely inconsistent at times.
The American has a game that most players would only dream of, sporting a booming serve and phenomenal groundstrokes that could put any player to the sword.
She established that at Wimbledon in 2015 where she made the quarterfinals in a stunning run that consisted of straight-sets wins over Karolina Pliskova, Samantha Stosur and Lucie Safarova before falling 6-3 6-7(3) 6-2 to Maria Sharapova.
Looking back, it’s unsurprising that her maiden run to a Grand Slam quarterfinal happened at Wimbledon, as her aggressive game is best-suited to the grass surface. She has also won her only two titles, on grass in s’Hertogenbosch in 2014 and again last year.
But her game is also suited to the fast and hard courts of the US Open and the Australian Open, where she is currently excelling.
The 25-year-old lost seven of her last 10 matches in 2016, but was in brilliant form in the Hopman Cup, only losing one singles match (to Daria Gavrilova) throughout the whole first week in Perth.
After four matches in Melbourne, she stands in the quarterfinals of a Grand Slam for the second time in her career, where she’ll meet Garbine Muguruza on Tuesday.
“It's an interesting matchup because she holds a different aspect to a playing style of she's an aggressor, as well. She is going to play that way, and no other way,” Vandeweghe said of Muguruza.
“For me it depends on if I can match it, as well as if I can beat her to that punch of getting first strike, first play.”
Vandeweghe’s run in Melbourne has been has been a special one, with the world No.35 taking out 17th seed Roberta Vinci 6-2 7-6(3) in the first round before another straight-sets win against Pauline Parmentier in the second.
The third round posed something a little more difficult, with former world No.5 Eugenie Bouchard on the other side of the net. The American took the first set before dropping the second and emerging from a break down in the third to claim a 6-4 3-6 7-5 victory to set up a match with No.1 Angelique Kerber in the fourth round.
After her win over Bouchard, Vandeweghe said her confidence is at a high when she plays at the back of the court. In that match she was brutal from the baseline, clubbing 40 winners, many of them on return. She also said she expects to win every match that she participates in.
“Last two, three years I have been riding such good confidence from playing from the back of the court,” she said.
“As well as having more confidence in my returns from playing more doubles,
“For me, if you go out on the court already thinking you're going to lose to anybody, you have already lost before you have taken a step out there and played the first point or started the warm-up.”
The American’s match against Kerber was sublime, as she claimed a 6-2 6-3 win over the defending champion.
Over recent years, the women’s draw in major play has seen many unseeded players go deep in Grand Slams, and the way Vandeweghe is playing, the American could sail straight through to the final with no troubles.
Who is Coco Vandeweghe? Why everyone is going loco for Coco at the Australian Open 2017
Vandeweghe is set to play former world number one Venus Williams in the semi-final after growing up watching her play tennis.
“It’s a dream to play someone you grew up watching," Vandeweghe said ahead of the semi-final on Thursday in Melbourne.
"But to do it at this stage of a Grand Slam is kind of crazy. I mean, I can't really put it into words.”
The hard-hitting American tennis player was inspired by Venus and once even asked for her autograph when she was young.
Vandeweghe said that she thinks it is “pretty cool” that she will go up against another American in the semi-final.
The brash sportswoman continued her impressive run today by defeating French Open champion Garbine Murguruza 6-4, 6-0 at the Australian Open.
It comes after tennis player pulled off the biggest upset of the tournament by beating world number one Angelique Kerber in style.
Vandeweghe has swaggered around the court at the Australian Open but admitted that she felt “nervous and scared” ahead of the match today.
But she said: “I think I don't shy away from a challenge necessarily. I never have. Growing up, I've always just been wanting to prove people wrong in a lot of different regards.”
Vandeweghe, from New York, credited her beauty queen grandmother’s advice for getting her success in tennis.
“My grandmother always said to me, ‘Fake it till you make it’,” she said. “Coming from a Miss America that basically oozed confidence, that’s a pretty good line.
“I had a divorced mother. I don’t really know my father at all. My grandparents helped raise me. That was really special for me.”
Her grandmother was crowned Miss America in 1952, while her grandfather played basketball for the New York Knicks and her mother was an Olympic swimmer.
Vandeweghe said: “We grew up in a competitive household. Everything was competitive, from card games, racing to the car first to get to the front seat.
“My grandfather would throw something at me when I was doing my homework just to make sure I’m quick and ready, do different things like that.
“It was just fun, stupid things like that.”
Vandeweghe’s previous best Grand Slam tournament was making the quarter-finals at Wimbledon in 2015.