He helped Valencia to beat Barcelona 4–3 on aggregate to win the Supercopa de España,[10] and netted a career-best 13 goals on the domestic front as the Che finished third.

Mendieta scored an early penalty in normal time to give his team a 1–0 lead, and also converted his attempt in the shootout,[13][4] being again named "UEFA Best Midfielder of the Year".

Mendieta was loaned to Barcelona for the 2002–03 season[18]– he started most of the fixtures, but the Catalans could only finish sixth[19]– and subsequently he moved to Middlesbrough,[20] choosing the Premier League club over offers from his homeland (Atlético Madrid and Athletic Bilbao) due to a desire to play in England.

[5] In his last two years, a string of injuries (including one which caused him to miss the 2006 UEFA Cup final)[4] and long spells of regaining match fitness relegated Mendieta to the substitutes bench.

He made his senior debut on 27 March 1999, coming on as a substitute for Juan Carlos Valerón in a 9–0 rout of Austria for UEFA Euro 2000's qualifying stages;[28] he was included in the list of 22 for the competition in Belgium and the Netherlands, helping the national side to reach the last eight.

[29] Despite his form slump at Lazio, Mendieta was picked for the squad at the 2002 FIFA World Cup, scoring one goal in three matches for the eventual quarter-finalists, against South Africa (3–2 win).

Fellow Bilbao-born Spain internationals Ander Herrera and Roberto Ríos had similar origins, learning their skills in the cities where their footballing fathers (Pedro and Eusebio respectively) were based professionally.

[6][36] He was a fan of music, and in particular had a passion for DJing;[36] he also appeared on-stage at the Benicàssim festival in 2015 during a set by the band Los Planetas, whose song "Un buen día" referenced him in its lyrics.