Nelson earned a spot on the U.S. team for the 2008 Summer Olympics in Beijing, by placing second at the U.S. Olympic Trials in Eugene, Oregon, with a time of 8:21.47. He competed as a member of U.S. track and field team in the men's 3000 m steeplechase, along with his teammates Anthony Famiglietti and Joshua McAdams. Nelson ran in the second heat against thirteen other athletes, including Famiglietti, and France's Mahiedine Mekhissi-Benabbad, who later won the silver medal in the final. He finished the race in eleventh place by six tenths of a second (0.60) behind Great Britain's Andrew Lemoncello, with a time of 8:36.66. Nelson, however, failed to advance into the final, as he placed thirtieth overall, and was ranked farther below four mandatory slots for the next round.