Xie, who was left off the Olympic team four years ago, coasted to a 21-1, 21-9 win over Taiwan's Cheng Sha-chieh at Beijing University of Technology Gymnasium.
"I didn't think the match would be so easy," said Xie. "I met her several times before and remember that it always went to three sets."
Xie had a first-round bye and will next face Olga KONON of Belarus in the third round. Konon defeated Slovenia's Maja Tvrdy 21-17, 21-14.
Xie combined powerful smashes with precision drop shots to send off the unseeded Cheng.
Defending Olympic champion Zheng, who is second-seeded, recovered from a shaky start to defeat Thailand's Salakjit Ponsana 21-23, 21-17, 21-7.
"I wasn't too worried after losing the first set," said Zhang, who also had a first-round bye." I've played her before so I knew what to expect.
Zhang is only seventh in the world rankings and has struggled with injuries this year but was picked over 2007 world champion Zhu Lin, who is third in the world rankings.
The 33-year-old Zhang was rusty in the first set but quickly took control of the match with smashes that were too powerful for her 29th-ranked opponent.
Zhang will next face South Korea's Jun Jae-youn, a 21-12, 21-14 winner over Chloe Magee of Ireland.
China won three of five gold medals in badminton at the Athens Olympics in 2004 and is expected to dominate on home soil.
Sunday was the first day China's players were in action and the capacity crowd was in full voice in support of their players, waving Chinese flags and shouting "Go China."
China's Lu Lan, who is third-seeded, overpowered Karen Foo Kune of Mauritius 21-3, 7-1. Kune was forced to retire with a leg injury.
In other matches, fourth-seeded WANG Cheng of Hong Kong coasted to a 21-7, 21-8 win over Eva Sladekova of Slovakia while eighth-seeded Wong Mew Choo defeated Kerry Lee Harrington of South Africa 21-4, 21-4.
Sixth-seeded Tine Rasmussen of Denmark defeated Akvile Stapusaityte of Lithuania 21-6, 21-8 and fifth-seeded Pi Hongyan of France downed Peru's Claudia Rivero 21-6, 21-9.
Seventh-seeded Xu Huaiwen of Germany posted a 21-17, 21-8 win over Finland's Anu Nieminen.
China's Lin Danis seeded No. 1 in the men's singles and will play his first match in the second round on Monday against unseeded Ng Wei of Hong Kong.
In women's doubles, defending Olympic champions Yang Wei and Zhang Jiewen of China defeated Indonesian pair Liliyana Natsir and Marissa Vita 21-19, 21-15 to advance to the quarterfinals.