Williams, the surprise silver medallist at last year's Athens Olympics, clocked 10.93 seconds to join men's gold medallist Justin Gatlin as a world champion.
Ethiopian Kenenisa Bekele stepped on to the track for the first and last time at this year's championships to retain the men's 10,000 title. Bekele confirmed after the race that he would not run in the 5,000.
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The fifth gold of the day went to Olympic silver medallist Ivan Tikhon who won the men's hammer with three throws in excess of 80 metres in difficult conditions for the field events.
The diminutive Williams deprived her heroine Gail Devers of a place in the U.S. team for Athens by a hundredth of a second.
"This was the biggest win of my career," she told reporters. "The Olympic silver is pretty good, but for me this is better.
"I had a very good start, and I knew that if I could just maintain my speed I would finish ahead. The rain made absolutely no difference for me. There was a hurricane out there tonight, but that is just my kind of weather."
ETHIOPIAN TEAM
Williams finished third in this year's American championships and looked impressive in finishing second to Frenchwoman Christine Arron at the Bislett Games in Oslo eight days before the start of the championships.
Bekele, already acclaimed as the best distance runner in history after his dominance on the track and over the cross country, pulled his compatriot Sileshi Sihine through on his way to the gold medal as he had in Athens last year.
Once again the Ethiopians ran as a team at the front, moving adroitly to counter the threat of the Kenyans, and easing away at the bell.
After the race Bekele said he was still in mourning for his 18-year-old fiancee who died in a training run last January and would not run the 5,000.
"It's been a very difficult year for me since the death of my fiancee. Also I don't think I can run three different races at this championship," he said.
"It was a very hard race because of the rain and we weren't able to work together as much as we would have liked. I'm happy we got two medals."
The 28-year-old Bergqvist, the bronze medallist at the last two worlds, cleared 2.02 metres on her first attempt to win her first global gold in the absence of Russia's Olympic champion Yelena Slesarenko who injured her foot in qualifying.
She then attempted Stefka Kostadinova's 18-year-old world record of 2.09 but failed with three attempts at 2.10.
Inzikuru stayed out of trouble at the head of the field in the steeplechase, although she looked in danger of drowning in the water jumps.
"I took the position because I don't like running behind others," she said. "I am so grateful to win the first ever medal for Uganda."
