It was not until 1998 that Kenteris took part in his first major international tournaments, when he took 9th place (semi finals) in both 400 m (45.74) and 4 × 400 m relay (3:06.48) at the 1998 European Championships in Budapest. He also took the 7th place at the 1998 IAAF World Cup in Johannesburg, in the 4 × 400 m relay race (3:03.95), representing the European team. In 1999, he continued by winning the 200 m (20.60) and 400 m (45.82) gold medals at the 1999 Greek Athletics Championships in Athens. His first European success was when he won the 400 m bronze medal at the 1999 European Cup in Paris with a time of 45.66. While Kenteris was eliminated in the 400 m heats of the indoor world championships, he returned that summer as a 200 m runner at the Outdoor World Championships in Seville. Kenteris won his heat # 5, defeating then 100 m world record holder Maurice Greene, but did not start the quarter-finals due to injury. The following year, Kenteris won the 4 × 100 m relay gold (40.46) at the 2000 Greek Athletics Championships in Athens, and also the 4 × 100 m relay silver (38.67) and 200 m bronze (20.48) at the 2000 European Cup in Gateshead.