It was not the most spectacular of fights with little action over the first few rounds.
As the fight progressed Guevara did pick the pace up and solid right hand shots began to land regularly.
Lopez was caught and briefly stunned in the seventh round as Guevara continued to attack.
Well behind on points and needing a knockout to win, Lopez upped the action in the last four rounds.
Guevara was briefly hurt in round 10 and narrowly avoided a knockout in the 11th round when a Lopez uppercut caught him and appeared to send him to the canvas only for the referee to rule that it was a slip.
Guevara held out in the 12th round to get the decision on the scorecards, prevailing with scores of 116-112 (twice) and 117-111.
The result sees Guevara improve is career record to 26-1-1 (17KOs). Lopez ended his five-fight winning streak to 25-6 (15KOs).
This was Guevara's second title defence after winning the crown with a 7th round knockout of Akira Yaegashi last year in Japan.