"This gold medal is the beginning of our career," Zhao said after their win in the mixed doubles final on Friday.
The duo, who are a couple off court as well as on, easily handled second-ranked Xu Chen and Ma Jin 21-11, 21-17 in an all-Chinese match that quickly gathered an air of inevitability.
The most excitement came immediately afterwards, when Zhang threw his shoes into the crowd and grabbed a Chinese flag to wave around Wembley Arena.
"Perhaps that was a bit over the top but I was so excited," he said.
Zhao didn't share in her boyfriend's enthusiasm, but she did call home to thank her parents, a sports school principal and tennis coach.
She admitted to being far more excited about her chance at a second gold medal on Saturday in the women's doubles, when she will face a Japanese pair.
"I have to keep calm, that will be a true challenge," Zhao said.
Meanwhile, the bronze-medal playoff revived one Olympic badminton tradition and ended another.
Joachim Fischer and Christinna Pedersen were too good in a 21-12, 21-12 victory over Tontowi Ahmad and Lilyana Natsir of Indonesia, winning Denmark's first Olympic medal in badminton since Athens. Denmark missed a badminton medal at the games for the first time in Beijing.
Denmark coach Lars Uhre said a medal and a semifinal were their targets in London.
"We have accomplished that in a very impressive way," Uhre said. "We feel we were very close to going to the final with this pair, and we are so far very proud of our team, everyone has performed.
"It's hard to be unhappy, and we hope for more," he added, knowing Matthias Boe and Carsten Mogensen were still to play their men's doubles semifinal.
Indonesia, on the hand, the best medal-winner after China with 18 including six golds, finished empty-handed at an Olympics for the first time and was set to return home to critical reviews about its decline in a national obsession.
Indonesia hasn't won the Thomas Cup since 2002, the Uber Cup since 1996 and the Sudirman Cup since 1989. It has one man in the top 10 and no women. Former Olympic and world champion Taufik Hidayat, who is retiring, has blamed players for a lack of commitment, and officials for politicking.
The pressure Ahmad and Natsir felt as their country's last hope in badminton came in the apology Natsir, a silver medallist in Beijing, felt was necessary after their match.
"We are really sorry," she said. "There was a real pressure on us for this match and we are really sorry we couldn't meet the target. We just have to accept the result as it is."
Fischer and Pedersen came together four years ago but their progress was stymied by Fischer's knees. He needed operations on both, the last in 2010 which sidelined him for six months and took longer to rebound from. When he was fit, the pair showed their worth by reaching five consecutive Super Series finals last year.
However, they were upset in the quarterfinals of the world championships by Ahmad and Natsir.
After losing to Zhang and Zhao in the semifinals on Thursday, when they led 19-18 in the third then Pedersen netted three times, they knew they had to get over their misery quickly.
"I didn't get any sleep," Fischer said. "This morning I was tired, and my body was killing me. But me and my partner and our coach, we promised each other we would do everything we can to win the match today, and we are proud to do it."
Fittingly, match point was won by Pedersen at the net. Pedersen, 25, to Fischer's 33, said they will continue for as long as his knees hold up.
"We won't say we will play for four more years," she said. "When Joachim can't play we will stop."