David Ferrer and Andy Murray, the top-two seeded players in the Mexican Open, advanced to the second round but American and third-seeded John Isner became the first major casualty of the tournament, losing 7-6, 7-6 to Croatia's Ivo Karlovic.
Ferrer, the favourite in Acapulco, had a convincing 6-2, 6-3 victory over Kazakh Mikhail Kukushkin while Murray overcame a sluggish start and claimed a 3-6, 6-1, 6-2 win over Pablo Andujar, from Spain.
"I had a difficult start, it was 10 minutes in the match and I was down 5-0, but I started to play more aggressively to get the win and hopefully I can have a good week here," Murray said.
"The first set was extremely challenging, he was dictating the points, but later on he was getting tired and put the pressure on him."
South Africa's Kevin Anderson downed Stephane Robert of France 6-2, 7-6 and will next play America's Sam Querrey. Also, Alexandr Dolgopolov, from the Ukraine, beat Canada's Vasek Pospisil 6-2, 6-2 and seventh-seeded Ernests Gulbis had a 6-1, 6-1 victory over Taiwan's Yen-Hsun Lu.