During the second half of the 2009–10 Ligue 1 season, he was called up to the first team by manager Claude Puel and appeared on the bench in the team's 1–0 victory over Montpellier on 2 May 2010.
Three days later, Lacazette made his first team debut in a Ligue 1 home match against Auxerre.
On 3 July 2010, Lacazette signed his first professional contract agreeing to a three-year deal.
Due to still having another year left on his aspirant (youth) contract, the contract would start on 1 July 2011.

Lacazette's successful campaign in the 2010 UEFA European Under-19 Championship saw the player draw interest from Italian club Roma.
He also drew praise from the media, alongside international teammates Yannis Tafer and Clément Grenier, for his dedication to the club after playing in the pre-season 2010 Emirates Cup match hours after playing in the final of the 2010 UEFA European Under-19 Football Championship.
Lacazette began the 2010–11 season training full-time with the first team.
He scored 6 goals in 12 2010–11 CFA matches for the club's reserve team.
He scored his first competitive goal for the first team on 30 October in a Ligue 1 home match against Sochaux.
His goal in the 69th minute gave Lyon a 2–1 lead, which would be the final score.
Three days later, Lacazette made his European club competition debut against the Portuguese club Benfica in a 2010–11 UEFA Champions League Group B away match, appearing as a substitute in the second half with Lyon trailing 4–0.
Minutes after coming onto the pitch, he assisted Lyon's opening goal, scored by Yoann Gourcuff in the 75th minute.
He also assisted Lyon's second goal, scored by Bafétimbi Gomis in the 85th minute.
Lyon, however, were unable to complete the comeback, losing 4–3.
On 7 December, Lacazette scored the first European club competition goal of his career in Lyon's final Group B match, the 88th-minute equaliser in the 2–2 home draw against Israeli club Hapoel Tel Aviv.
During the second half of the 2009–10 Ligue 1 season, he was called up to the first team by manager Claude Puel and appeared on the bench in the team's 1–0 victory over Montpellier on 2 May 2010. Three days later, Lacazette made his first team debut in a Ligue 1 home match against Auxerre. On 3 July 2010, Lacazette signed his first professional contract agreeing to a three-year deal. Due to still having another year left on his aspirant (youth) contract, the contract would start on 1 July 2011.
Lacazette's successful campaign in the 2010 UEFA European Under-19 Championship saw the player draw interest from Italian club Roma. He also drew praise from the media, alongside international teammates Yannis Tafer and Clément Grenier, for his dedication to the club after playing in the pre-season 2010 Emirates Cup match hours after playing in the final of the 2010 UEFA European Under-19 Football Championship. Lacazette began the 2010–11 season training full-time with the first team. He scored 6 goals in 12 2010–11 CFA matches for the club's reserve team. He scored his first competitive goal for the first team on 30 October in a Ligue 1 home match against Sochaux. His goal in the 69th minute gave Lyon a 2–1 lead, which would be the final score. Three days later, Lacazette made his European club competition debut against the Portuguese club Benfica in a 2010–11 UEFA Champions League Group B away match, appearing as a substitute in the second half with Lyon trailing 4–0. Minutes after coming onto the pitch, he assisted Lyon's opening goal, scored by Yoann Gourcuff in the 75th minute. He also assisted Lyon's second goal, scored by Bafétimbi Gomis in the 85th minute. Lyon, however, were unable to complete the comeback, losing 4–3. On 7 December, Lacazette scored the first European club competition goal of his career in Lyon's final Group B match, the 88th-minute equaliser in the 2–2 home draw against Israeli club Hapoel Tel Aviv.
Alexandre Lacazette