The 2003 season saw Zersenay establish himself as an emerging force in cross country: he broke into the top ten at the 2003 IAAF World Cross Country Championships, and finished in the top three in all of his six races in Europe that winter. A 5000 metres win at the KBC Night of Athletics brought Zersenay an Eritrean record of 13:11.07, and a place at the IAAF World Championships in Athletics. At the 2003 World Championships, he improved his record further to 13:05.57 and finished in eighth place in the 5000 metres final. More improvements came at the World Half Marathon Championships in Vilamoura, Portugal, where he recorded a personal best of 1:01:26 to finish in seventh position.