The American duo allowed their opponents few chances in quarter-final routs, with Pegula dispatching fatigued compatriot Ashlyn Krueger 6-4, 2-0 through retirement.
Krueger, a lucky loser from qualifying, was feeling the effects of nine matches over the past 12 days in Brisbane and Adelaide.
World number seven Pegula, last year's US Open finalist, played doubles with Krueger this week and knew her partner was tired.
"It's never fun to win with a retirement," said the 30-year-old, who will face either Yulia Putintseva or world number 13 Diana Shnaider for a place in the final.
"I knew she had a tough singles yesterday. But coming out you never know what to expect, she was still playing amazing tennis."
Russia's Liudmila Samsonova earned her first top-10 win in over a year when she ousted world number eight and second seed Emma Navarro, 6-4, 6-4.
Samsonova will face either third seed Daria Kasatkina or Madison Keys next.
In the men's draw, Paul duplicated his final-four place in Adelaide from 2020 with a 6-3, 6-4 defeat of Australian Rinky Hijikata.
He will now face Canadian fifth seed Felix Auger-Aliassime, who defeated American Marcos Giron 7-6 (7/3), 6-3.
"That's a big match," said Paul, who is seeking a fifth ATP Tour title.
"The more time on court the better for me."
Serbia's Miomir Kecmanovic surged into the last four with a 6-2, 6-3 defeat of French qualifier Benjamin Bonzi.
His reward is a clash with American second seed Sebastian Korda, who had a walkover after Australia's Thanasi Kokkinakis pulled out.
