Fans invaded the pitch and confronted players as Belgrano defeated River Plate 2-0 in Wednesday's first leg of their relegation playoff - a result that put Argentina's most successful club on the brink of a humiliating relegation.

Just after Belgrano went ahead 2-0 early in the second half, dozens of hooligan fans - at least one wearing a mask - ripped through a fence, raced across the pitch and taunted and shoved River Plate players.

Referee Nestor Pitana halted the match for 20 minutes as police with batons and shields cleared the troublemakers from the field and stands of the Cordoba stadium.

The return match is scheduled for Sunday at River Plate's 50,000-seat Monumental stadium. The likelihood of violence is high, with River Plate facing relegation to the second division for the first time in its history.

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 to overcome the 2-0 deficit in one of the club's most important games in its 110-year history.

River has won the Argentine first division title 33 times - more than any club - and relegation had been regarded as unthinkable for the Buenos Aires giants.

Violence menaces almost every club match in Argentina, with the outbreaks often taking place outside the stadium - usually before or after the match.

This time it happened in the middle of the game with hooligans tearing through a chain-link fence topped with razor wire. One masked fan shoved River Plate defender Adalberto Roman, who ignored the taunt and walked away. The dozens of invaders then crawled back through the fence, or climbed it with with wild cheers from other fans.

Thirteen fans have died in football-related violence in just over a year in Argentina. The AFA is often criticized for ignoring the violence, but argues it's a social problem and not a football problem.

The incident took place just a minute after Cesar Pereyra gave Belgrano a 2-0 lead in the 50th. Cesar Mansanelli had scored Belgrano's first goal in the 26th.