The Jamaican set the record of 9.74 seconds and then was back on the track some 90 minutes later to run 9.78 in the final.
It was an emphatic return for Powell, who was a disappointing third at the Osaka world championships last month behind American rival Tyson Gay and Derrick Atkins of the Bahamas.
Powell's compatriot Michael Frater came second with a time of 10.03 seconds and Norway's Jaysuma Saidy Ndure was third with 10.10.
Irving Saladino had an easy time in the long jump thanks in part to the absence of injured Italian Andrew Howe, the Rieti athlete who pushed the Panamanian all the way in Osaka. The world champion won with a leap of 8.31 metres.
Other 2007 world champions who won their events were Kenya's Janeth Jepkosgei in the women's 800 metres, Russia's Yekaterina Volkova in the women's 3,000 metres steeplechase and Cuba's Yargelis Savigne in the women's triple jump.
In the hammer, Japan's Olympic champion Koji Murofushi beat world champion Ivan Tikhon of Belarus by one centimetre with a throw of 82.62 metres.
Russia's Anna Chicherova dashed the crowd's hopes of seeing a home winner by clearing 1.98 metres in high jump, three centimetres more than Italy's Antonietta Di Martino, the woman she shared silver with in Japan.