The contest marked the first time he battled it out on his own against a pro-democracy opponent. Twice before, he had been included in slates of his party.
He went around Sham Shui Po yesterday to thank residents for their votes. He had been a district councillor there for over a decade. His victory, he said, was the people's approval of his service as a district councillor.
Asked if he was surprised, Cheng said the narrow win would be a constant reminder that the pro-establishment camp should keep working for the people at all times.
Au Nok-hin, who left the Democratic Party last year, said his win was a pyrrhic victory for the pan-democracy camp.
Au said the pan-democrats paid a heavy price - referring to the two seats lost.
"This isn't my victory. The honor belongs to every one in the camp," he said. "I wouldn't have won if they hadn't put all their efforts into helping my campaign."
Au promised to take the oath properly to prevent any disqualification of lawmakers from happening again.
He said he would not join any political groups but was looking forward to communicating with different pan-democrat parties.
Au said following up on complaints about Paul Chan Mo-po's budget would be his first priority.
The winner of the New Territories East, Gary Fan Kwok-wai, rebutted criticisms that he had frosty relations with others in the pan-democracy bloc. He said he is thanking all members of the camp for showing great team work in supporting him.
He promised that his party, the Neo Democrats, would return the favor by helping other pan-democrats when necessary.
Fan said his victory proved that some people agreed with his manifesto - including his opposition to the national anthem law and the co-location plan for the West Kowloon high-speed railway station.
Meanwhile, Tony Tse Wai-chuen of the architectural, surveying, planning and landscape functional constituency, said he was glad to return to Legco.
He said he would use his professional knowledge to monitor government policies, including a follow up on the illegal structures scandal involving justice chief Teresa Cheng Yeuk-wah.