Messi made his senior Barcelona debut in 2004. He appeared in a competitive first-team match against Espanyol on 16 October 2004, entering as a substitute at the age of 17.
The debut came after Messi had progressed through Barcelona's youth system and Barcelona B. Manager Frank Rijkaard promoted him to the first team during the 2004–05 season, where he initially wore the No. 30 shirt. His brief appearance immediately marked him as one of the club's most exciting young prospects.
There is one distinction that often causes confusion. Messi had already played for Barcelona's first team in a friendly against Porto in November 2003, when he was 16. However, 2004 is the standard answer for his official or competitive senior debut, which is what most football histories and quiz questions mean by “senior debut.”
Messi made nine first-team appearances for Barcelona during that debut season and scored his first senior goal against Albacete in May 2005. Barcelona won La Liga that season, giving the teenager an early league title before he became a regular starter.