The 22-year-old American -- the world leader this season -- timed 13.10 seconds having led from the start.
Sergey Shubenkov, world champion in 2015, took silver in 13.15sec whilst Frenchman Pascal Martinot-Lagarde finished third in 13.18sec.
- Mayer trailing -
The opening rounds of the decathlon meanwhile saw France's reigning world champion and world record holder Kevin Mayer battling Canadians Damian Warner and Pierce LePage in the multi-discipline event.
Mayer opened the defence of his title with a personal best in the 100m, clocking 10.50sec to grab 975 points.
The Frenchman followed it with a season's best leap in the long jump before erupting in celebration after launching a throw of 16.82m in the shot put.
After five events, however, Warner is in the gold medal position with 4,513 points, with LePage just behind on 4,486pts.
Mayer remains firmly in contention with 4,483pts heading into Thursday.
In the heptathlon, Britain's Katarina Johnson-Thompson is locked in a thrilling duel with Belgium's reigning Olympic and world champion Nafissatou Thiam.
Johnson-Thompson recorded personal bests in the shot put and 100m hurdles as well as a season's best of 23.08sec in the 200m to finish the day on 4,138 points.
With the final three of seven disciplines remaining, Johnson-Thompson leads Thiam by 96 points.
The competition concludes on Thursday with the long jump, javelin and 800m.
Thiam will aim to eat into Johnson-Thompson's lead in the javelin, which is traditionally one of her British rival's weaker events.
Elsewhere Wednesday, the men's 400m witnessed a shock with Michael Norman, the world's fastest man over the distance this year, bowing out in the semi-finals.
Norman, 21, trailed home last in his semi-final with a time of 45.94sec.
Norman later revealed he had been struggling with a mystery injury to the lower half of his body for the past two months.
"My body gave me warning signs today and I listened to them and made the executive choice to slow down instead of risking injury," he told reporters.
"I've always approached each new challenge as it presented itself. Today my body got the best of me."