Born in Calahorra, La Rioja, Ezquerro emerged through the youth ranks of CA Osasuna, playing two second division seasons with the Navarrese before signing with Atlético Madrid for the 1996–97 campaign.

Lack of playing opportunities with the Colchoneros prompted a January 1998 move to RCD Mallorca, which Ezquerro helped achieve runner-up accolades in the Copa del Rey in his six-month stint.

Subsequently, he joined Athletic Bilbao,[2] with whom he appeared in his first UEFA Champions League games while establishing as one of the most promising forwards in Spain's top flight, notably scoring in a 3–0 derby home victory over Real Sociedad on 9 April 2005.

[3] His stellar form in 2004–05 – 47 official matches, 19 goals, including a hat-trick in a 7–1 away rout of Standard Liège for the season's UEFA Cup group stage[4]– led to Ezquerro signing for FC Barcelona in a period of 3+1 years, on a free transfer.

During his debut season for Athletic, Ezquerro won his sole cap for Spain, in a UEFA Euro 2000 qualifier against Cyprus, which ended with a 2–3 away loss and the sacking of coach Javier Clemente, on 5 September 1998.