Assefa set a blistering early pace, gradually shaking off any competition to pulverise Kenyan Brigid Kosgei's record of two hours 14 minutes and four seconds set in 2019.
Britain's Mo Farah won a record sixth successive Great North Run after setting his personal best time on Sunday. The Olympic gold medallist raced ahead of Ethiopian Tamirat Tola in the final mile to cross the line in 59 minutes and six seconds.
After biding his time for much of the race, the British four-time Olympic track champion surged to the lead in the final four miles and broke Ethiopian Mosinet Geremew to shatter the European marathon record of 2:05:48 despite wet and sometimes windy conditions.
Kenyan Brigid Kosgei broke Paula Radcliffe's 16-year-old women's marathon world record but former Alberto Salazar coached athletes, including Mo Farah, were never a factor in the Chicago Marathon.
The sport's governing body (WA) said that with immediate effect and for elite competition only, road shoes must have soles no thicker than 40mm and not contain more than one rigid, embedded plate.