The Jamaican Commonwealth champion set the record in his heat at the Rieti IAAF Grand Prix.
"It is a very fast record. It is to remind my friends that Asafa is still here," he told reporters.
Powell had previously shared the record of 9.77 with American Olympic champion Justin Gatlin, who has been banned for eight years for doping pending the result of an arbitration hearing.
At the Osaka World Championships, Powell finished third behind American Tyson Gay and Derrick Atkins of the Bahamas in the final.
The 24-year-old admitted at the time that he had given up during the Osaka race but said he would make amends by breaking his world record before the end of the year. 
"I've been with my coach and working hard to get back to normal," Powell said on Sunday. "The last 40 metres were very strong. I executed it and did what I came to do today."
The Jamaican, who won silver in the Osaka relay as Gay and the US team took gold, has never won a global title.
He was disqualified for a false start in the quarterfinals of the 2003 world championships after setting the fastest time of 10.05 in the heats.
Powell then finished fifth in the 2004 Olympic final behind Gatlin before missing the 2005 worlds through injury.
However, he won the Commonwealth 100 metres title in Melbourne in March last year and had run 9.77 three times, in June 2005, June 2006 and Aug. 2006, before this latest record.