Nethaneel Mitchell-Blake missed the national record by one-hundredth of a second as he became only the third Briton to run sub 20 seconds for 200m.
The 22-year-old clocked 19.95 seconds representing Louisiana State University at the Southeastern Conference (SEC) Championships in Tuscaloosa, Alabama.
John Regis set the British record of 19.94 in 1993, while Adam Gemili is the only other Brit to go sub 20.
“I aspired to go under 20 seconds,” Mitchell-Blake told BBC Sport.
He described his achievement as “overwhelming”, adding “to be part of the upper echelons is something I’m definitely proud of”.
Regis also clocked a 19.87-second time over 200m which was never ratified, and had already competed in two Olympic Games by the time he ran under 20 seconds.
Sub-20 in a third event of the day
Mitchell-Blake clocked his time having already won the 100m as well as anchoring his university to victory in the 4x100m at the SEC Championships.
His time puts him ahead of Adam Gemili (19.98) in the all-time British 200m rankings and he was visibly emotional, wiping away tears when approached for an interview on the track.
“The 200 is my favourite event,” Mitchell-Blake – the 2013 European junior champion – told BBC Sport.
“The Rio Olympics is definitely something I’m looking forward too. The NCAA championships is in the coming weeks and my first priority. Then I’ll come back to the UK and try to compete for a spot on the team.”
Chijindu Ujah and James Ellington have also already run under the 20.50-second Olympic A standard in 2016 and athletes with the qualifying time will race at the British Championships in June in order to earn a place on Team GB at Rio 2016.