Duplantis was the overwhelming favourite after soaring to 6.27m and shattering the world record for an 11th time in Clermont-Ferrand last month, and at Nanjing's Cube the 25-year-old Duplantis completed a century of jumps over six metres.
The twice Olympic champion comfortably scaled 6.05m for the 100th vault over 6.00m and despite a rare blip in his first attempt at 6.10m, he joined Sergey Bubka and Renaud Lavillenie as a triple world indoors champion.
Greece's Emmanouil Karalis pushed Duplantis hard but had to be content with silver after clearing 6.05m and American Sam Kendricks took bronze with 5.90m.
Jakob Ingebrigtsen found himself boxed in midway through the men's 3,000m final but the Norwegian expertly extricated himself with bursts of speed to finish in 7:46.09 and stay in the hunt for a 1,500m and 3,000m double.
That feat has been achieved only once at the indoor worlds, by Ethiopian great Haile Gebrselassie in 1999, but the 24-year-old Ingebrigtsen will fancy his chances over the shorter distance on Sunday.
"It was a little bit of a fight, but I was confident that I can make a move in the last 100m and win," Ingebrigtsen said.
"I don't enjoy the 1500m warm-up, but the racing is fun and that's what I'm going to do tomorrow, have a lot of fun."
Ethiopia's Berihu Aregawi was second with 7:46.25 while Australia's Ky Robinson finished third in 7:47.09.
Freweyni Hailu of Ethiopia claimed gold in the women's 3,000m final with a time of 8:37.21, finishing ahead of American Shelby Houlihan (8:38.26) and Australia's Jessica Hull (8:38.28).
"I was sick at home before coming to Nanjing, so I stayed at the back to conserve myself before making my push," Hailu said.