The pair met in the flyweight final at the Jakarta Asian Games in 2018, with Chang winning a tight decision.
In a scrappy rematch at the Hangzhou Gymnasium, it was Pang who did the better work to get a deserved result, even though the judges were split 3-2.
Several times, the boxers wrestled each other to the canvas in an ugly contest. Chang conceded the better fighter won.
“Last time we fought it was at a different weight so I think today was a completely new contest,” said the Chinese fighter.
“I should have done better,” added Chang, who was fifth in the 51kg class at the Tokyo Olympics.
“I will now try my best to prepare for the Paris Olympics and focus on training every day.”
However, the women’s middleweight final went according to plan for the vociferous home support as Li Qian took a comfortable unanimous points decision over the gutsy Indian Lovlina Borgohain.
In another scrappy contest, Li had the greater strength and landed the cleaner blows.
It is not just medals at stake in boxing in Hangzhou, but also Olympic qualification for Paris next year.
There are 20 women’s berths available in six weight divisions, and 14 places in seven divisions for the men.
Amateur boxing great Hasanboy Dusmatov eased to a 4-1 split decision against Japan’s former bantamweight world champion Tomoya Tsuboi.
The Uzbek entered the ring to chants of “Hasanboy, Hasanboy” and made an immediate statement of intent by landing a big straight left flush on the chin of the Japanese.
Tsuboi fought back to edge the final round but it wasn’t enough against the 30-year-old Olympic champion from 2016.
Dusmatov is now one win away from adding the only gold medal missing from his collection in the 51kg division.
But the flyweight world champion will have to do it the hard way – tomorrow’s final will be his third fight in two days.
He was scathing about the schedule after his second tough fight in less than 24 hours.
“It’s hard. I’m tired and aching and my face has bruises, with no time to recover,” he told AFP.
“I can’t eat properly to refuel because I have to make weight every day. We should not have to do this.”
He will face Thitisan Panmot for the flyweight gold medal after the Thai won a split decision against North Korea’s So Chon Ryong in the other semifinal.
In other action, Felix Marcial from the Philippines, a bronze medallist at the Tokyo Olympics, knocked out Syria’s Ahmad Ghousoon in the second round of their middleweight semifinal.
He faces China’s Tanglatihan Tuohetaerbieke in tomorrow’s gold medal bout.