Peng's presence during the Games had been a matter of speculation since the IOC said it planned to meet with her in Beijing.
Serena Williams voiced concern for fellow tennis player Peng Shuai, who has not been seen publicly since she accused a former vice-premier of China, Zhang Gaoli, of sexual assault.
Peng could be seen in the stands wearing a black knit hat with the Olympic rings on them and a black coat with the Chinese flag.
Chinese tennis star Peng Shuai, whose whereabouts have been a matter of international concern for weeks, attended a tennis tournament in Beijing on Sunday.
The Indian ace, who made it to the main draw of the Family Circle Cup through the qualifying rounds, won the first set 6-2, but failed to sustain the pace in the next two sets, which she lost 2-6, 2-6.
Yao said he and Peng had known each other for nearly 20 years. However, he did not comment directly on the controversy that flared up last year after Peng, a former world No. 1 doubles player, appeared to allege that a former vice premier, Zhang Gaoli, had sexually assaulted her in the past.
An outcry over the whereabouts of Chinese tennis star Peng Shuai escalated on Friday as the Women's Tennis Association (WTA) said it was prepared to pull its tournaments out of China if they were not satisfied with the response to her sexual assault allegation.
Djokovic says Peng situation horrifying, says tennis must unite.
The United States and Britain had also called for China to provide proof of Peng's whereabouts.
Chinese tennis star Peng Shuai said on Sunday that she had never accused anyone of sexually assaulting her, and that a social media post she had made early last month had been misunderstood.
In her now-deleted post on China's Twitter-like Weibo, Peng had written "why did you take me to your house and force me into having relations with you?", though she also described the relationship with Zhang as an on-off one that was also consensual.
Tennis great and founder of the WTA Billie Jean King was among those who applauded the announcement.
The Taiwanese-Belgian duo saved match points on the way to claiming a 3-6, 7-5, 9-7 win on Centre Court.
Winter Olympics will be staged by a country that has grown far wealthier, more powerful
Women's No 1 Serena Williams remained on track for her 60th career title as she powered past Peng Shuai 6-2, 6-3 while Rafael Nadal launched the defence of his Madrid Open title.
Azarenka said she believed getting vaccinated was the socially responsible thing to do
In the women's doubles event, the Indo-Chinese duo of Sania and Peng Shuai will take on Croatian professionals Petra Martic and Donna Vekic.
Maria Sharapova marched into the semi-finals of the Cincinnati Open after crushing Australian Samantha Stosur 6-3, 6-2 on Friday to set up a last four meeting with fellow-Russian Vera Zvonareva.
India's Sania Mirza and her Russian partner Elena Vesnina on Thursday advanced to the women's doubles semifinals of the Dubai Duty Free Tennis Championships with a hard-fought victory over Maria-Jose Matrinez Sanchez and Shahar Peer in Dubai.
Caroline Wozniacki gained a valuable confidence boost ahead of next week's French Open when she beat last year's Roland Garros winner Francesca Schiavone 6-4, 4-6, 6-3 in their Brussels Open semi-final on Friday.
Following Sania Mirza's quarter-final appearance in the Family Circle Cup last week, the Indian tennis ace jumped 17 places to 73rd position in the latest WTA singles rankings issued on Monday.
Sania Mirza and her Russian partner Elena Vesnina notched up a straight-set win over Ji Zheng and Peng Shuai to enter the final of the Family Circle Cup WTA event in Charleston, USA.
World number one Caroline Wozniacki moved into the quarter-finals of the Qatar Open with a 6-3, 6-2 win over Russian Nadia Petrova but third seed Francesca Schiavone was upset by China's Peng Shuai on Wednesday.
Rafael Nadal and Kim Clijsters swept into the Australian Open third round on Thursday as Serbia's Jelena Jankovic became the first top-10 player to exit the tournament. After three days of scares but no upsets at Melbourne Park, former world number one Jankovic, the seventh seed, was dumped out 7-6, 6-3 by Chinese upstart Peng Shuai.
Top seed Maria Sharapova delivered an enigmatic performance but still advanced to the quarter-finals of the Auckland Classic with a 6-3, 7-5 victory over Renata Voracova of the Czech Republic on Wednesday.
Former world number one Jelena Jankovic was reduced to despair at her poor shot selection after slumping to a shock 7-6, 6-3 loss to China's Peng Shuai in the second round of the Australian on Thursday.
Serena and Venus Williams both booked their places in the third round of the Sony Ericsson Open with victories at Key Biscayne in Miami on Saturday. World number one Serena did not sparkle but still had little trouble in her 6-2, 6-3 victory over compatriot Alexa Glatch. Serena's sister Venus got off to a slow start but found her form to defeat spirited Israeli Shahar Peer 6-3, 6-3.
World number two Dinara Safina battled into the fourth round of the WTA event in Indian Wells on Sunday, beating Peng Shuai of China 7-5, 6-4. Fourth seed Vera Zvonareva of Russia booked her place in the last 16 with a routine 6-3, 6-1 win over Czech Petra Kvitova.
Serena Williams eased her way into the fourth round of the Australian open on Saturday with a 6-1, 6-4 win over China's Peng Shuai. She will meet Victoria Azarenka, who knocked out former champion Amelie Mauresmo.
China reached the Fed Cup semi-finals for the first time with a 3-2 victory over France.
Chinese veteran Peng Shuai beat American Alison Riske 7-6(3), 6-2 in the final of the Tianjin Open to capture her first Tour title on Sunday.
Former French Open champion Michael Chang is no longer coaching China's Peng Shuai but still believes he could help Chinese chances of winning medals at next year's Beijing Olympics
Top seed Svetlana Kuznetsova overcame an error-ridden performance to beat China's Peng Shuai 6-2, 3-6, 6-4 on Thursday to advance to the third round of the Sony Ericsson Open on a clear and cool day in Key Biscayne, Florida.
Holders Russia will play Spain in the Fed Cup final after both teams made light work of their semi-final opponents on Sunday.
Five-times champions Spain surged to a 2-0 lead over China in their Fed Cup semi-final in Beijing.
A tired looking Maria Sharapova bowed out of the third round of the $6.6 million China Open on Wednesday, beaten 6-2, 6-4 by China's Peng Shuai to the delight of the crowd at the Olympic tennis centre.
China's top two Li Na and Zheng Jie will miss next month's Fed Cup tie against holders Italy to help other players qualify for the 2008 Beijing Olympics, according to a senior China Tennis Association (CTA) official.
Lindsay Davenport tasted defeat for the first time in a year on Saturday, losing 6-3 7-5 to second seed Jelena Jankovic in the China Open semi-finals.
Amelie Mauresmo made an unspectacular return to tennis after a two-month layoff with a 6-2, 6-2 victory over Romania's Ioana Raluca Olaru at the China Open.
The world number one beat China's Peng Shuai 7-5, 6-2 in the third round.