Gamboa's 2004 Olympic Boxing results were:
Gamboa fought Gilberto Luque on January 5, 2008, at Bally's Hotel & Casino in Atlantic City, New Jersey. Gamboa sent his opponent to the canvas after only 30 seconds with a left hand. After two more knockdowns the referee stopped the fight. On February 22, 2008 in Fort Lauderdale, Florida, he made his American television debut against Johnnie Edwards. Gamboa knocked Edwards down in the first 30 seconds of the fight after connecting with a left hand to the head. Edwards got up, but was met with left hand punches from Gamboa ending with two consecutive right hands that knocked Edwards down for the second and final time as the referee moved in and halted the fight in round one.
On May 17, 2008, at Buffalo Bill's Star Arena in Primm, Nevada, Gamboa fought Darling Jimenez. Gamboa started off well in the first three rounds of the fight, swarming Jimenez and hitting him with punches over and over. Gamboa looked flustered in the fourth round and began showing signs of fatigue. He got careless and was knocked down by a right hand behind the ear from Jimenez. Gamboa got up and finished the fight strong, winning by unanimous decision. After the fight, Gamboa’s promoter Ahmet Öner fired his trainer Osmiri Fernandez, replacing him with Ismeal Salas. On July 18, 2008, Gamboa scored a first round technical knockout victory over Al Seeger in a fight that took place at Buffalo Bill's Star Arena in Primm, Nevada. A left hook to the body set up a right hand that landed across Seeger's face, causing him to collapse backwards flat onto the canvas. The referee stepped over Seeger without bothering to count, officially stopping the bout.
On October 5, 2008, Gamboa stepped up in class, yet again, and fought Marcos Ramirez, a Kansas City featherweight boasting an undefeated 25-0 record in Temecula, California. Gamboa exhibited amazing handspeed and quick combination punching in the first round before he was dropped by what was revealed to be an elbow to the chin by Ramirez. Gamboa quickly came to his feet and resumed fighting until the bell rang to signify the end of the round. In the second round, Gamboa picked up where he left off and knocked Ramirez down with a fast right uppercut, followed by another combination. Ramirez let the referee administer the eight count before rising to his feet. Gamboa then finished the fight by pressuring Ramirez into the ropes and landing a left hook to the body, followed by a right uppercut to the jaw. The referee stopped the fight, although it seemed like his count seemed too quick and Ramirez was back on his feet by the count of ten. Gamboa's record improves to 12-0 (10 KOs).