Michalak earned further caps for France that year during June. He was an unused bench replacement in a match against Argentina, but was then moved into the starting line-up for subsequent matches against Australia, both of which France lost. In 2003 he started at scrum-half for France in their Six Nations match against Italy in Rome at Stadio Flaminio. France won the match with Michalak also scoring his first try for the national team. He played in one other Six Nations match that year, starting against Wales in Paris, where he scored another try in the 33–5 victory. Toulouse proceeded to win the 2002–03 Heineken Cup, defeating fellow French team USA Perpignan 22–17 in the final. Michalak was then included in the national squad for the June tests prior to the 2003 World Cup in Australia. He was not used in France's first match against Argentina, but came off the bench in the second of two. He then started in the following match against the All Blacks, where he scored eight points with his kicking in the loss. He earned subsequent caps in matches against Romania, scoring 14 points with his boot, and against England where he scored 12 of France's 17 points in the one point victory. Michalak was subsequently included in France's squad for the 2003 Rugby World Cup and made his World Cup debut against Fiji at Suncorp Stadium in Brisbane during the pool stages, where he scored 26 points. He scored over 20 points in another match against Japan, including a try. He also scored a try in the subsequent game against Scotland and was rested for the final pool match against the United States. Michalak was superb in France's 43–21 quarter-final win over Ireland in Melbourne, landing all nine goal attempts (four conversions and five penalties) for a personal haul of 23 points. France would go on to face World Cup favourites England in the semi-final. On a rainy night in Sydney, Michalak endured a nightmare game with the boot, scoring only once from five attempts before eventually getting replaced as France, despite scoring first, went on to lose the game 24–7. Despite this, Michalak still finished the tournament as the second-highest points scorer with 101 points. Only Jonny Wilkinson (113) scored more. The following year, Michalak played in four of France's Six Nations fixtures all in the starting line-up. He was not used in the match against Italy. Toulouse also made it to the final of the 2003–04 Heineken Cup, though they were defeated by the London Wasps.