Betsen's finest moment came during the 2002 Six Nations Championship, in the match against , when his relentless man-marking of Jonny Wilkinson eventually resulted in the fly-half's replacement and paved the way for a 20–15 victory. Later, England's coach, Clive Woodward, said of Betsen: "“He is the only player that I can say was the single-handed reason we lost a match." France went on to win the Grand Slam and Betsen was named France's International Player of the Year. He was an automatic selection for the 2003 Rugby World Cup and scored France's only try in the semi-final loss to England.