During his Olympic visit, Nasution was not considered an elite swimmer, but also a sport fan, posing for pictures and talked with Australian legends Grant Hackett and Ian Thorpe, as well as Americans Tom Malchow, Lenny Krayzelburg, and Gary Hall, Jr. Meeting with his sporting heroes, he recalled his greatest Olympic moment: "It was a lot of fun. They were guys I heard about and idolized growing up but after meeting them, they're just normal guys. They were all nice." At the 2001 Southeast Asian Games in Kuala Lumpur, Malaysia, Nasution collected only two medals in swimming, a silver in the 200 m breaststroke (2:22.82) and a bronze in the 100 m breaststroke (1:06.04). Shortly after the Games, Nasution left his native Indonesia to spend his two-year residency and training in Australia under famed swimming coach Denis Cotterell. He also accepted a full athletic scholarship to attend Chaffey College in Rancho Cucamonga, California, and later became a member of the school's swim team under head coach Mike Dickson. While playing for Chaffey, he received California State Swimmer of the Year honours twice, posting wins and personal bests in three events: 500-yard freestyle (4:30.82), 400-yard individual medley (3:57.08) and 200-yard breaststroke (2:02.93). Nasution also helped the school's freestyle relay team to a fourth-place finish, and the medley relay to sixth. Despite of his training schedule and education in the United States, Nasution continued to compete for the Indonesian squad in international tournaments. He set an Indonesian record in the 400 m freestyle (4:00.57), and later helped his teammates Richard Sam Bera and twins Felix and Albert Sutanto capture a silver medal in the 4 × 100 m freestyle relay (3:29.46) at the 2005 Southeast Asian Games in Manila, Philippines. Two years later, Nasution added two more medals, a silver and a bronze, to his career hardware in a medley double at the 2007 Southeast Asian Games in Bangkok, Thailand. When Indonesia hosted his fifth Southeast Asian Games in Jakarta four years later, Nasution took home a bronze medal for the host squad in the 400 m individual medley, posting a lifetime best of 4:31.27.