Her compatriot, Kendra Harrison, was just behind her and Danielle Williams from Jamaica was third.
Once Ali had finished her lap of honour, the women’s 4x400 relay team triumphed shortly followed by the men to take the haul to 14.
The women won their bauble in a world leading time of 3:18.92.
The victory provided Dalilah Muhammad with her second gold of the championships and Allyson Felix with a record extending 13th medal.
Muhammad, 29, won the 400m hurdles on Friday night and though Felix did not feature in the final quartet, she collected her gold for running in earlier rounds.
“This is the one chance we get to come together to compete as a team,” said Muhammad. “There’s definitely a different vibe to it. Before the race we’re supporting one another. We usually do, but in a relay, it’s just a little bit extra special.”
Poland were second and Jamaica finished third.
Overall, 43 countries won medals during the 10 days of competition dominated by American athletes.
The 4x400 men’s team underscored that ascendance with a convincing win in the season’s best time of 2.56.59.
Michael Cherry and Wilbert London, who ran the second and third legs respectively, both won their second gold of the championships after their success in the 4x400m mixed relay on 29 September.
Rai Benjamin, who won silver in the 400m hurdles, ran the anchor leg. “I’m happy that my teammates put me in a great position," said the 22-year-old. "My job was just to hold it and finish.
“I’ve been waiting for this for a while … to go out and represent my country. It’s what I’ve always wanted to do. It was a good week and to run anchor and bring it home is a perfect way to end.”
Of the other prizes, Anderson Peters from Grenada took the men’s javelin with a throw of 86.89m and Joshua Cheptegei edged a thrilling finale to the men’s 10,000 metres.
He kicked for the line with 150 metres left but Ethiopia’s Yomif Kejelcha stayed with him. They battled for supremacy down the home straight and the Ugandan prevailed in a time of 26:48.36.
Kenya’s Timothy Cheruiyot collected the men’s 1500m and Malaika Mihambo added the world long jump title to the European crown she claimed on home soil in Berlin last August.