Korir improved his times during the 1983 season, but finished only seventh at the first World Championships. Korir continued to improve in 1984 and after winning his semi-final at the Los Angeles Olympics, he established himself as a serious contender for the gold medal. In the Olympic final, Korir was always with the leaders, and when he started his sprint for home with just over half a lap remaining, the rest of the field were unable to respond.