Argentina's most decorated team have been in dire straits for the last two years and in the local system of points averages over three seasons to determine relegation they need every win they can get to avoid the drop in May.
Former Argentina World Cup forward Ariel Ortega crossed from the left and young striker Rogelio Funes Mori headed home for a 1-0 win over Tigre, the team that crushed them 5-1 in the final match of last season.
River were fortunate and had goalkeeper Juan Pablo Carrizo, back from a spell playing in Europe, to thank for keeping them in the match but coach Angel Cappa claimed the win was deserved.
"I like winning and more so the way we did today, at the end," said Cappa. "We deserved the victory and to have scored more goals, but I'm aware we have to improve."
Tigre, direct rivals in the fight against relegation, did not help their own cause by being too cautious in the second half after a first 45 minutes in which they had the better of the game.
River's Monumental stadium was packed with a crowd of about 70,000.
River fans were anxious for, and ultimately a bit disappointed with a first glimpse of the side rebuilt by Cappa, who made nine signings during a long pre-season while the World Cup was being played in South Africa.
Cappa praised his old guard of 36-year-olds Ortega and former Parma and Lazio midfielder Matias Almeyda, who came back last season from three years in lower division football.
"Almeyda had a colossal performance and Ortega was decisive as always," Cappa told a post-match news conference.
22-SECOND GOAL
Arch-rivals Boca Juniors, also looking to recover after a poor 2009/10 season under new coach Claudio Borghi, needed an equaliser from striker Lucas Viatri for a 1-1 draw away to Godoy Cruz in the Andean city of Mendoza.
Title holders Argentinos Juniors, who won the Clausura under Borghi in May, were upset 2-1 at home by Cappa's former club Huracan.
Juan Sebastian Veron netted a 71st minute penalty to give Estudiantes a 1-0 away win over Newell's Old Boys in Rosario.
Alejandro Delorte headed a goal for promoted Olimpo against Banfield after 22 seconds but the home side, who won last season's Apertura in December for their first ever title, recovered to win 2-1.
The strike was not as quick as the fastest goal in a top flight match in Argentina, scored by Carlos Seppaquercia after seven seconds for Gimnasia-La Plata against Huracan in 1979.
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