Just one month to go for general elections in Latin America's second largest economy and it is turning out to be a contested election after all.

The candidate of Mexico's Institutional Revolutionary Party (PRI) Enrique Pena Nieto’s seemingly unbeatable lead is slipping with the left wing Party of the Democratic revolution (PRD) now looking like its candidate has a fighting chance.

One poll out this week puts Andres Manuel Lopez Obrador just four percentage points behind the leader. The governing National Action Party (PAN) candidate Josefina Vasquez Mota is continuing to slip, even in strongholds like the State of Jalisco and Nuevo Leon.

With a very large number of voters still undecided, the race is now wide open and young people - who make up roughly one third of the vote and who have mobilised against the two traditional parties - may be the deal breakers.

In another development, there is a significant sign of a split within the feared Zetas drug cartel.

On Friday, just a few blocks from the governor's building, a large and well produced banner with photographs was placed over a pedestrian walkway. In it, one faction of the leadership denounces Heriberto Lazcano-Lazcano, the top gun, as a traitor who has been eliminating other important “cadres” in the organisation.

According to the US Drug Enforcement Administration (DEA), in 2009 the leader of the Zetas was Heriberto Lazcano-Lazcano. It clearly calls for members to switch their allegiance to another member of the group, former Mexican Special Forces Lieutenant Arturo Guzman Decena.

This almost certainly means there will be a particularly vicious outbreak of violence within Mexico's most bloodthirsty organised crime organisation, at a very sensitive time.