Yakimenko's debut senior competition was the team event of the 2002 World Championships in Lisbon, where he won a gold medal together with Sergey Sharikov, Stanislav Pozdnyakov and Aleksey Frosin. He claimed his first individual medal at the 2003 European Championships in Bourges: his winning streak was interrupted only in the final by his captain, four-time Olympic champion Pozdnyakov. He came away with a silver medal, to which a team gold medal was added a few days later. He was defeated in the second round of the World Championships, but Russia retained his World title.