He made his Bundesliga debut in dramatic fashion on 25 February 2007 against league leaders Schalke 04. With starting goalkeeper Hans-Jörg Butt serving a suspension following a red card, Adler saved ten shots on goal, repelling Schalke's repeated attacks. A breakaway goal by Stefan Kießling in the 85th minute gave Leverkusen a 1–0 upset victory. Leverkusen manager Michael Skibbe praised Adler's "world-class saves". He stopped Schalke's record of 13 games unbeaten, Stuttgart's record of five games unbeaten and Hamburger SV four-game winning spree with a saved penalty kick against Rafael van der Vaart. He ended up making 15 appearances in all competitions for the first team and two appearances for the B team. On 8 March 2008 Adler made his first international appearance, losing the UEFA Cup round of last 16 first leg against RC Lens. He finished the 2007–08 season with 44 appearances in all competitions for the first team.