Mexican champions Tigres UANL scored a controversial goal after the ball appeared to have gone well out of play, beating Queretaro 1-0 for their first win of the Clausura championship.
Guadalajara crashed 3-1 at Chiapas in another of Saturday's matches in the season's second championship while Estudiantes UAG coach Jose Luis Salgado resigned after two defeats.
Tigres, with four points from two matches, went ahead in the 40th minute when Carlos Salcido whipped the ball from the touchline when it looked half a metre out, Elias Hernandez crossed and Brazilian defender Juninho scored.
"The damn ball was a metre out! ... I feel more annoyed after seeing it on the telly," said angry goalkeeper Liborio Sanchez of Queretaro's "Gallos".
"It's clear Tigres can't score a goal against Gallos, only with the referee's help," he wrote on his Twitter account (@liborio31).
Queretaro coach, former Paraguay striker Jose Cardozo, told reporters: "Tigres are a great team who don't need help. The referee was very unfair with us."
Guadalajara are playing well below the standard they set in the qualifying phase of the Apertura championship and finished with nine men after their frustration boiled over in the final minutes of their match at Chiapas.
Captain Hector Reynoso, who scored a first-half equaliser, was shown a straight red card after elbowing Colombia striker Jackson Martinez, scorer of Chiapas' third goal.
Coach Fernando Quirarte, whose job is on the line after two defeats in a row according to Mexican media, said: "I'm calm because my team played a great match. Unfortunately, the result doesn't say so.
"I could be contradicting myself but sometimes the result doesn't reflect what happened on the pitch," he told reporters.
Salgado, who took charge at relegation-threatened Estudiantes in November for their final match of the Apertura, announced his resignation the day after his side lost 2-0 at home to leaders San Luis.
"Given the results we haven't got and which the club needs and deserves, we took the decision to step aside and hope someone can come to help the club," he told a news conference on Saturday.
San Luis, the only team with six points, can be caught on Sunday by America or Toluca who clash at the Azteca.
Santos Laguna, who lost the Apertura final to Tigres last month, have signed Spanish midfielder Marc Crosas, a product of Barcelona's youth scheme who has played for Olympique Lyon, Celtic and Volga Nizhny Novgorod. The 24-year-old was not in their squad for Saturday's 2-1 win at Atlante.