Lopez, a lover of Salsa music, had an amateur record of 37-1, after which he jumped to the professional ranks. His professional debut came January 18 of 1985 in Cuernavaca, Mexico with a three round knockout over Rogelio Hernandez. This was the start of a streak of knockout wins that reached seven. Then, in 1986, he was extended to the ten round distance in Mexico City by Herminio Ramirez, but he still won that fight by a unanimous decision. In a rematch between Lopez and Ramirez, Lopez once again won on points.
In 1987 and 1988, Lopez won six more bouts, and in 1989, he won six before challenging for a minor, non world title: The WBC continental America's Strawweight title. He won that belt by knocking out Rey Hernandez in five rounds in Mexico City during his final bout of the 1980s. Lopez was then ranked number 1 among the world Strawweight challengers by the WBC.
Lopez started the decade of the 1990s, by beating Jorge Rivera by a knockout in eight at Texas to retain his regional belt, and then he followed with a ten round decision over Francisco Montiel. After the win versus Montiel, his world championship bout versus WBC world Strawweight champion Hideyuki Ohashi was signed, and in October of 1990, Ricardo travelled to Japan, where he became world champion by knocking Ohashi out in five rounds.
Next came a string of 22 defenses in a row, which is a record for the Strawweight division, and at the time, the third longest string of defenses in the history of boxing, after Joe Louis' 25 and Dariusz Michalczewski's 23. Lopez's string was stopped only because he struggled to make the 105-pound limit late in his career, and finally moved up to light flyweight (108 pounds) for his final three fights. Among the boxers he defeated were former world champion Kyun Yung Lee, future world champions Samart Sorjaturong and Kermin Guardia, and fringe contenders Ala Villamor, Andy Tabanas and Manny Melchor. On the night of August 23, he unified his WBC belt with the WBO championship at the Madison Square Garden by knocking out Puerto Rico's Alex Nene Sanchez in five rounds in front of a Pay Per View audience. He was promptly stripped of the WBO belt when it became public knowledge that he presented the belt to his father.
On March 7 of 1998, he suffered the only blemish in his professional record when he attempted to unify his WBC belt with the WBA championship against Nicaragua's Rosendo Alvarez in front of another Pay Per View audience at Mexico City. Lopez was dropped in round one, but he got up and kept fighting. In round five, there was a clash of heads, and the fight had to be stopped in round seven because of the cut on Lopez's forehead. The fight went to the judges' scorecards, and they had the bout scored a draw. There was an immediate rematch, and the second time around, Lopez was able to edge out a split decision win at Las Vegas.
After renouncing his world strawweight titles, Lopez went up in weight, and in 1999, he received a shot at the IBF world Jr. Flyweight champion Will Grigsby, and Lopez became world Jr. Flyweight champion, beating Grigsby by a decision in 12.
He fought just two more times after defeating Grigsby. The first was against former world champion Ratanol Vorapin on December 2 of 2000, knocking him out in 3 rounds to retain his belt as part of the Felix Trinidad-Fernando Vargas fight undercard. In his last fight, on September 29, 2001, he scored an eighth-round knockout of Zolani Pethelo. A layoff of 15 months followed.
On sunday, November 23 of 2002, Ricardo called all major news outlets in Mexico to announce his retirement from boxing. Among the people who attended the conference were Julio Cesar Chavez and Marco Antonio Barrera. He retired with a record of 50 wins, 0 losses and 1 draw, joining Rocky Marciano as the only world boxing champions ever to retire undefeated.
Lopez, who is an avid autograph signer, once intended to record a salsa CD, and had many proposals to star in telenovelas on Televisa.