He made his Argentine Primera División debut on 11 June 2011, as a 59th-minute substitute for Cristian Raúl Ledesma in a 0–1 home defeat to Arsenal.

[5] On 26 June 2015, Alario became River Plate's fourth signing of the season, joining the Buenos Aires-based club on a four-year contract for a fee of 2.25 million US Dollars.

[7] Eleven days later, as a substitute, he equalised for a 1–1 draw away to Paraguay's Club Guaraní in the second leg of the Copa Libertadores semi-finals, converting a pass from Tabaré Viúdez to send River through 3–1 on aggregate to their first such finals since 1996.

[8] On 5 August, in the second leg of the final after a goalless first, he finished Leonel Vangioni's cross at the end of the first half to open the scoring as his team won 3–0 against Tigres UANL.

[17] Alario had his first appearance on 1 September 2016, coming from the bench replacing Lucas Pratto in the 71st minute during a World Cup Qualifier 2018 match against Uruguay.