After returning to Arsenal, Martínez was an unused substitute as Arsenal won the Community Shield on 10 August 2014, with a 3–0 win over Manchester City at Wembley Stadium. He made his debut in the Champions League soon after, helping Arsenal defeat Anderlecht 2–1 in the group stage. He then made his Premier League debut as a 2nd half substitute, replacing the injured Szczęsny against Manchester United at the Emirates Stadium on 22 November. With injuries to backup goalkeeper David Ospina, Martínez played his second Champions League game on 26 November, keeping a clean sheet in a 2–0 victory over Borussia Dortmund. His "faultless" performance in the match led to him being named in the UEFA Team of the Week. He made his first Premier League start on 29 November against West Bromwich Albion, and also started against Southampton four days later; he kept two clean sheets as Arsenal won both matches 1–0.