Alonso was born in
Vicente López,
Buenos Aires province, but grew up in the poor suburb of
Los Polvorines. An attacking
midfielder, he rose through the ranks of River's youth divisions as the team was undergoing its infamous dry spell (18 years, 1957 to 1975, without a
championship title). When
Angel Labruna took the reins in 1975, Alonso was the team's anchor and holder of the No. 10 jersey. With reinforcements
Roberto Perfumo and
Ubaldo Fillol, and the maturing of players like
Daniel Passarella,
Carlos Morete,
J. J. López and
Reinaldo Merlo, Alonso led the squad that won both the
Metropolitano and the
Nacional tournaments of 1975, ushering in a series of seven local titles in the period 1975–1981. In 1976, Alonso was transferred to
Olympique Marseille, but he was unsuccessful. River Plate arranged for his return in 1977. Between the years 1979–1981, River won four local titles, and became one of the most expensive teams in the world, with a first team (Alonso-
Luque) playing in league games and an equally prestigious second team (Carrasco-
Ramón Díaz) used mostly in
Copa Libertadores matches. During the
1981 "Nacional" tournament (which River would eventually win), Alonso often clashed with then coach
Alfredo Di Stéfano (who seldom selected him for the first team and instead put younger players such as
Carlos Daniel Tapia and José María Vieta in his position). After the
Nacional, Alonso was put on the transfer list and was sold to
Vélez Sársfield on 1982. After playing alongside veteran
Carlos Bianchi, he returned to River Plate once again for the
1984 season. Many talented midfielders emerged from River Plate's youth system during Alonso's reign, including
Alejandro Sabella,
Néstor Gorosito and
Pedro Troglio. Alonso was a key player of the successful team of
1985–86 that won River Plate's first
Copa Libertadores and
Intercontinental Cup. In 1985, his main partner was
Enzo Francescoli. By the time he retired, he had scored 166 goals in 464 matches. ==National team==