Wozniacki, the runner-up at Flushing Meadows in 2009, yesterday dismissed 13th-seeded Italian Sara Errani 6-0, 6-1 and is back in the semi-finals of a major for the first time since the 2011 US Open.
China's Peng, in the quarter-finals of a major for the first time in her 37th attempt, made similarly short work of Swiss teen Belinda Bencic 6-2, 6-1.
Peng joined two-time Grand Slam champion Li Na and Zheng Jie as the only Chinese to reach the last four of a Grand Slam.
"It's a little bit too exciting," she said. "I love tennis, I love to play, but it's a long time, the career. It's tough. Sometimes I've thought to give up and stop playing because I don't know if I can make it or not.
"My coach and my parents always told me to fight and not give up -- that today was coming."
Wozniacki was similarly convincing on a windy night on Arthur Ashe Stadium court, where towels from the players' chairs and stray plastic bags had to be corraled.
Errani, who boasts a top-speed serve of less than 90 mph (144.84 Km/h) couldn't hold once in six service games.
She was unable to capitalize on any of four break points in the opening game of the match and after fighting for that hold Wozniacki was rolling.
"It was really tricky conditions with the wind but I tried to stay aggressive," Wozniacki said, calling the opening game "very important".
"You always go out there and are a little bit nervous. I served really well after that."