Some of Mexico's presidential candidates cried foul late Wednesday after the country's second-largest broadcaster said it would air a soccer game instead of the first presidential debate Sunday.

The decision this week by broadcaster TV Azteca SAB sparked a brawl involving the candidates, the country's political parties and electoral authority, pundits, its soccer league and sports fans.

The move led to accusations that TV Azteca -- and its billionaire owner, Ricardo Salinas Pliego -- is protecting front-runner Enrique Pena Nieto, the candidate of the Institutional Revolutionary Party, Mexico's former ruling party.

Pena Nieto enjoys a 20-point lead in most polls over his nearest rival and has by far the most to lose by a bad debate performance. With the election only two months away, his rivals hope a debate stumble could slow his momentum.

"If the debate is not broadcast on open television, it's going to be obvious that the networks want to impose the next president of Mexico," according to Andres Manuel Lopez Obrador, the candidate of the leftist Party of the Democratic Revolution, who polls put in third place.

Lopez Obrador, who narrowly lost the 2006 election, called on Mexico's election agency to force broadcasters to carry the debate. The agency said it was considering such a move.

The debate over the debate underlines the continuing influence that the country's television duopoly, made up of TV Azteca and No. 1 broadcaster Grupo Televisa SAB, exerts on its politics. TV Azteca, controlled by Salinas, has about 30 percent of Mexico's open television market, while rival Televisa controls the rest.

The two broadcasters have long been among the country's most important power brokers, trading access to the airwaves in exchange for protecting their business interests.

Some analysts say that both Azteca and Televisa want to help elect Pena Nieto in exchange for protecting their duopoly by ensuring that no other firm can build a viable third or fourth broadcaster. In the past, both companies acted to block new entrants, according to rival media companies and analysts.

Azteca had no immediate comment Wednesday, but in the past, it rejected any accusations that it tried to cut deals to protect its business interests. Pena Nieto's campaign also has rejected any such quid pro quo.