Rivers Plate is 90 minutes away from being relegated for the first time after the record 33-time Argentine champion lost 0-2 at modest Belgrano in the first leg of a playoff on Wednesday.

Goals either side of halftime from midfielder Cesar Mansanelli and striker Cesar Pereyra gave the second-tier Nacional B side the victory that put it on the verge of a place in the top flight.

River, whose last title was in the second half of the 2007-08 season, finds itself in the dire situation as a result of its poor three-season points average that determines relegation in Argentina.

The match was interrupted for 20 minutes after River went two goals behind early in the second half. Some of its fans broke a hole in the perimeter fence and stormed onto the pitch in the city of Cordoba.

The fans remonstrated with their own team's players, demanding more effort from them, before being ejected and order was gradually restored.

The return match is scheduled for Sunday at River's 50,000-seat Monumental Stadium in Buenos Aires. The likelihood of violence is high and the Argentine Football Association will likely consider playing the second leg in an empty stadium; a blow to a team that would be counting on the support of its fans in one of the club's most important games in its 110-year history.

River needs to get back on level terms and will survive with an aggregate draw as the result favors first division sides.

Earlier, Gimnasia beat nine-man Huracan 2-0 in a one-off match at the Bombonera to qualify for the other playoff, while condemning the loser to relegation.