Complex sentence: Desvaux started his career with Unión de Santa Fe in 2001, the club were relegated from the Argentine Primera in 2003, but Desvaux stayed with them.
Split into simpler sentences: Desvaux started his career with Unión de Santa Fe in 2001 while the team played in the Primera División Argentina. In 2003 his club was relegated from the Argentine Primera but Desvaux stayed with them.