In the 2000 Summer Olympics in Sydney, Australia, Nelson earned a silver medal after coming in first place in the 2000 Olympic Trials for shotput. Going into the Games, Nelson was the favorite to win, having won every major shotput event in the summer of 2000. His throw of 21.21 m (69 ft 7 in) was just three inches (8 cm) short of the winning throw by gold medalist Arsi Harju.
Nelson's personal best is 22.51 (73 ft 10 in), which he threw in 2002. At that time, this was the fourth longest throw in U.S. history and the ninth farthest ever in the world.
Nelson also earned a silver medal in the shot put finals at the 2004 Summer Olympics in Athens, Greece. The shot put was held in a spectacular setting at the original Stadium of Ancient Olympia, bringing Olympic competition back to the venue for the first time in over 1,000 years. Nelson jumped out in front of the field with his first throw of 21.16 m (69 feet 5 inches), and held the lead going into the sixth and final round. As the leader, Nelson was scheduled to be the last thrower in the round and thus, the competition. The holder of the 2nd place throw, Yuriy Bilonog of the Ukraine was scheduled to throw second to last. If Nelson remained in first place after Bilonog's final throw, he would know that he had won his first gold medal and his last throw would become moot. It was not to be. Yury Bilonog stepped up and threw 21.16 m (69 feet 5 inches) to tie Nelson for first place with his sixth throw. To break a tie, the competitors' second best throws are compared and unfortunately, Nelson had fouled every throw since his competition-leading first throw. Nelson entered the ring for his final throw and unleashed what looked to be a gold medal winning 70 foot throw, but unfortunately fouled by stepping on the line to the left front of the circle. Thus, by virtue of the tie-breaker and his superior second-best throw, Yuriy Bilonog won the gold medal and Nelson had to settle for his second consecutive Olympic silver medal. He initially protested vociferously to the officials but later realized that he did in fact foul, and apologized for his emotional reaction. Nelson's silver medal was the first track and field medal for the United States in the 2004 Summer Olympics. Nelson finally achieved his dreams of a major world title when he won gold at the 2005 World Athletics Championships with a throw of 21.73 meters. He has qualified to compete in his third straight Olympics in Beijing, placing third at the 2008 US Trials.