According to Official Guinness Records,
During the 1968 Summer Olympics held in Mexico City, the African-American sprinter Jim Hines earned the title of ‘fastest man on the planet’ when he broke the long-standing 10-second barrier in the 100 m event. With a time of 9.95 sec, Hines stormed to Olympic gold and established a 100 m world record that remained unbeaten for 15 years. Astonishingly, he would go on to better his time at the very same Olympics, running the anchor leg of the 4 x 100 m relay event in just 8.2 sec.
Jim Hines achieved a time of 9.9 sec in his semi-final at the AAU championships held in Sacramento on 20 June 1968, but this was manually timed.
For a complete list of 1968 records, please visit 1968 Guinness Records in Mexico.