Kesler participated in his first International Ice Hockey Federation-sanctioned event at the 2002 IIHF World U18 Championships in Piešťany and Trnava, Slovakia. He finished the tournament with seven points in eight games, including two goals in a 10–3 defeat over Canada in the final round. The Americans won their first U18 title, with Kesler being awarded the Best Player Award for the tournament. Later that year, Kesler was named to the United States national junior team for the 2003 World Junior Ice Hockey Championships in Halifax and Sydney, Nova Scotia. He finished the tournament second in team scoring behind Zach Parise with seven points in seven games as the United States lost 3–2 to Finland in the bronze medal game. During the tournament, Kesler was twice named the United States' player of the game: in their quarter-final game versus the Czech Republic and in the bronze medal game versus Finland.