Zhang had finished no better than sixth in any World Cup appearance this season and when the starting order was put together for Thursday's race she was placed in the seventh of the 18 pairs that competed at the Olympic skating oval.
The top-ranked skaters are usually placed among the final few pairings in a speed skating event.
Zhang turned in a stunning time of 1:14.02, which was more than three seconds faster than any of the skaters who had gone before.
It was clear that her time would contend for a medal and it wound up being fastest of all.
Irene Wust and Margot Boer, two members of the juggernaut speed skating team from the Netherlands, won the silver and bronze medals. Wust had won gold earlier in these Olympics in the 3,000-meter race and Boer captured the bronze over 500 meters.
Wust was timed in 1:14.69 and Boer in 1:14.90.
Hong completed a big day for China in the world of speed skating. In the women's short-track 500-meter event Li Jianrou avoided a three-skater crash to win the gold medal.
The women's 1,000-meter race was only the second of six speed skating competitions in the Olympics that was not won by a skater from the Netherlands.
Even though the Dutch could not win the gold in this race, they have grabbed 12 of the 18 medals handed out thus far in the sport. Those 12 medals represent the entire Olympic collection for the Netherlands.