Pastore's debut was on 15 August in the Coppa Italia, while his debut in Serie A came eight days later. His breakthrough game was on 4 October against Juventus, when he assisted Edinson Cavani's goal in a 2–0 win, appearing in all the websites and national newspapers. He scored his first Serie A goal on 30 January 2010 in a 2–4 away defeat to Bari. In his first season at Palermo, Pastore proved himself as being a promising but inexperienced youngster, playing mostly as a second-half substitute under head coaches Walter Zenga and, later, Delio Rossi.
Pastore was subsequently called up by Maradona again for a friendly game against Germany, but did not make an appearance. His official debut was against Canada on 25 May 2010, and he was subsequently included by Maradona in Argentina's 23-man squad for the 2010 FIFA World Cup. On 22 June, he made his FIFA World Cup debut when he came on the pitch in the 77th minute against Greece, replacing Sergio Agüero. Argentina won the match 2–0. On 27 June, he was again substituted on against Mexico in the 87th minute, this time replacing Maxi Rodríguez. Argentina won the match 3–1.
An elegant, creative and technically gifted advanced playmaker, with excellent dribbling skills and close control, Pastore is capable of playing in several offensive roles, due to his ability to both score and create goals. Although he is usually deployed as an attacking midfielder due to his vision, passing and striking ability from distance, he is also capable of functioning as a winger, as a supporting striker or even as a forward, and has also been deployed in more withdrawn midfield roles on occasion, operating as a central midfielder, as a deep-lying playmaker, or even as a mezzala, due to his work-rate, creativity, skill, and physical attributes, despite his lack of notable pace. A talented, strong, quick and hard-working right-footed player, his playing style has drawn comparisons to Kaká, Zinedine Zidane, Zlatan Ibrahimović and one of his childhood idols, Enzo Francescoli, although Pastore has stated that his main influence is compatriot Juan Román Riquelme. Nicknamed "El Flaco" (like Francescoli before him) due to his tall, slender build, he was regarded as a highly promising player as a youngster, and in 2010, Don Balón named him as one of the 100 best young players in the world born after 1989. Despite his talent, however, he is known to injury prone, and has also drawn criticism in the media for being inconsistent.