In sweltering conditions, top seed Pavlyuchenkova overcame falling 4-1 behind in the first set to eventually edge past Chang, 64 64, and set up a semifinal with Vania King.
"I had a bit of a slow start today," Pavlyuchenkova said. "It was a very difficult temperature - really hot and humid. It was really tough conditions. Compared to the previous days when I played much later, it was difficult.
"It wasn't my best match today and Chang had some confidence after winning those first few matches. She went out there and was playing really well. I kept going, and I kept trying to find my energy. I'm happy I pulled it out."
King was also forced to dig deep in her quarterfinal, overcoming a mid-match blip to see off fellow American Coco Vandeweghe. After racing through the opener, the No.4 seed was punished for a momentary lapse in concentration midway through the second, as the big-serving Vandeweghe converted her first break point before serving out the set.
The final set was another tight affair, but it was King who held her nerve when it mattered, breaking decisively in the final game to advance, 61 36 64.
"She's much bigger and much stronger than I am and she comes up with some amazing shots, but I just hung in there," King said. "I tried to be aggressive when I could and tried to take my chances when I could.
"I'm definitely playing a lot more solid and a lot stronger than I was in the first round. Once you get through each match you start to get better. It's just a matter of competing well against your opponent."
Rybarikova arrived in Washington fresh from a quarterfinal run in Baku and has carried this form into the opening rounds, advancing to the last four without dropping a set. Her latest win came over qualifier Jana Cepelova who she saw off, 62 64.
Stephens, meanwhile, who had struggled in the previous rounds, produced her best performance of the week to defeat Canadian teenager Eugénie Bouchard, 64 64.
"I thought I played solid, I didn't give away a lot of free points and I served pretty well," Stephens said. "She played well and we had some really good rallies. I was pleased with the way I played and I could not have played much better.
"I love being out on the court and I love to compete. I'm pleased with the way I am playing and happy to be out on the court and just being able to play. Win or lose I am just happy to be playing."