The number of people wounded in Sunday's attack in the central state of Puebla also rose from six to 11 after officials received reports from hospitals, authorities said.
Witnesses told investigators that armed men arrived in three vehicles, got out and opened fire on players and the crowd in the town of Acatzingo, 170 kilometres southeast of Mexico City.
The first two fatalities were players. A 46-year-old man succumbed to his wound at a hospital yesterday, the prosecutor's office said.
"There are reports that the origin of the incident was a dispute over control of thefts of oil or gas," the office said in a statement.
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One of the dead, Jose Luis Velez Robles, who died on the field, was apparently "linked to (these) thefts," it said.
In May 2011, Velez and two other people were held by police in a house where 22,000 litres of fuel of "suspicious origin" were found, the statement said, adding that the suspects had been handed over to the federal attorney general's office.
Late last month, four people died when gunmen linked to fuel thefts opened fire in the village of La Purisima, an area where rival gangs seek to control illegal pipeline taps.
State-run energy firm Pemex discovered some 5,000 illegal taps in pipelines across the country in 2015.