The 28-year-old Texan finished in 19.66sec at the US Olympic trials in Atlanta on Sunday night, surpassing the Italian's 19.72 set at altitude in Mexico City on 12 September, 1979. Jeff Williams finished second in 20.03 and the 1992 Olympic champion, Michael Marsh, was third in 20.04.
Johnson said: "We've got three of the best runners in the world right here. So it's going to be tough again in another month at the Olympics. Whenever you've got tough competition, I think the world record could go down even further. I feel like I'm capable of running 19.5."
Allen Johnson equalled the second fastest 110m hurdles ever at the trials. His time of 12.92sec was one-hundredth of a second off Colin Jackson's world record of 12.91.