The nine-time Grand Slam winner, who last prevailed Down Under in 2003, will now face unseeded compatriot Coco Vandeweghe for a place in the final.
Williams edged her meeting against Pavlyuchenkova 6-4 7-6(3), with the first set proving to be a war of attrition as both players failed to keep hold of their serve.
Despite losing serve in the third and seventh games, Williams still did enough to get over the line and took a huge step towards a rare last-four outing in Melbourne.
It proved to be a similar case in the second set as, after winning a mammoth second game, Pavlyuchenkova failed to truly push on and could only rescue a tie-break.
Williams took six points on the spin to earn the victory and set up a clash with Vandeweghe, who eased past seventh seed Garbine Muguruza 6-4 6-0 in the other quarter-final.
Vandeweghe held throughout the match and picked off her opponent to get over the line in a time of less than 90 minutes.