Mares vs. Perez

On May 22, 2010, Mares challenged undefeated IBF Bantamweight Champion and the No. 4 ranked Bantamweight Yonnhy Perez (20-0) for his title.^[6] The bout ended in a 12-round majority draw with one judge scoring it 115–113 in favor of Mares while the other two scored it 114-114 even. The majority of the press at ringside scored the bout in favor of Mares.^[7]

This marked the launch and the climb to success with world-famous trainer, Clemente Medina.

Bantamweight Tournament

Mares vs. Agbeko II

On December 3, 2011, Mares and Agbeko fought a rematch due to their controversial first fight. While the second fight proved to be much less controversial, there were still several low blow warnings from the referee to Mares. Though Agbeko had moments in the fight where he outboxed Mares from the outside, Mares closed the distance and outworked Agbeko throughout the fight, and landed the more significant punches. Mares was awarded a unanimous decision win, by the scores of 118-110 from all three judges. .

Super Bantamweight title

In Mares' next fight, he moved up to the super bantamweight division, fighting former world champion Eric Morel for the vacant WBC Super Bantamweight title. The fight took place on April 21, 2012, at a catchweight of 120 lbs. Mares effectively out worked, landed more, and landed the harder punches throughout the fight, with Morel showing significant signs of his age. Mares won a unanimous decision by the scores of 120–107, 119–109, and 119–109 to claim his first Super Bantamweight title.

Mares vs. Moreno

Mares' next fight took place on November 10, 2012, against the world No. 1 ranked bantamweight and then No.10 pound-for-pound Anselmo Moreno. Mares started the fight off fast, applying relentless pressure on Moreno, forcing Moreno to the ropes for the majority of the early rounds. Moreno still had his moments while the two were in the middle of the ring, landing clean shots, while Mares attempted to out work Moreno and attack his body while on the ropes. In the 5th round, Moreno was having success staying off the ropes when he could, and out boxing Mares in the center of the ring. Near the end of the round, Mares trapped Moreno on the ropes and landed a hard straight right hand, which ultimately sent Moreno to the canvas for the first time in his career. The following middle rounds of the fight, Mares seemed in control working the body and landing his hard overhand right, relentless pressuring Moreno for the majority of the rounds. In the 11th round, Moreno was docked a point for pushing Mares' head down while Mares rushed him on the ropes. This was seen as very controversial, given that Mares and Moreno both had been warned several times throughout the fight and only Moreno was docked a point. After the point deduction, Moreno effectively out pointed Mares in the middle of the ring during the final rounds and even successfully traded with Mares against the ropes, while Mares seemed to tire the final couple rounds.

Mares was awarded the Unanimous decision by the scores of 116–110, 116–110, and 120–106.

Mares vs. De Leon

Mares moved up to 126 lbs to fight WBC Featherweight champion and Ring No. 2 ranked Featherweight, Daniel Ponce de León in the Mayweather-Guerrero undercard on May 4, 2013, and knocked down de León in the second and ninth rounds en route to handing him a TKO loss at 2:20 of the ninth round, winning the WBC featherweight title in the process.^[8]

Mares vs. González

Mares defended his WBC Featherweight title against underdog former world champion Jhonny González on August 24, 2013, at the StubHub Center in Carson, California. Mares lost the fight in a first-round TKO to González. The referee stopped the fight after Mares was knocked down for the second time in the first round.^{[9][Video 1]}

Mares would leave his management company, Espinoza Boxing Club, as well as trainer Clemente Medina. He would train with Virgil Hunter for his next fight before returning to Clemente Medina.

Mares vs Cuellar

On December 10, 2016, Mares fought Jesus Cuellar for the WBA "regular" featherweight title. Mares won tia fight via split-decision, with two of the judges scoring the fight in his favor, 117-110 and 116-111 while the third judge saw Cuellar as the winner, scoring it 115–112 in favor of the Argentine.^[10]

Mares vs Gutierrez

In his next fight, Mares fought Andres Gutierrez. Mares retained his title be winning the fight via technical decision in the tenth round.^[11]

Mares vs Santa Cruz

On June 9, 2018, Mares fought WBA super featherweight champion Leo Santa Cruz in a long-anticipated rematch. In a brutal and exciting fight, both fighters were throwing and connecting at a similar rate. All three judges agreed on who is the winner of the fight, with all three scoring it in favor Santa Cruz, 117–111, 116-112 and 115–113.^[12]