Seattle Sounders have made it three wins from three outings in the CONCACAF Champions League.
The Colombian opened the scoring in just the third minute in Alajuela with his side dominating proceedings until the stroke of half-time when the home side were awarded a penalty which was converted by Jose Cancela.
But Seattle got a deserved second ten minutes after the re-start when Montero tapped home from close range after Herediano keeper Daniel Cambronero could not hold onto Roger Levesque's attempt.
The Sounders are now the only side of the 16 with a perfect record and head coach Sigi Schmid was delighted after the match, especially with the form of Montero who has scored four in his last three in all competitions.
"Goal scorers, sometimes they are streaky," Schmid said. "He is hitting a good streak and we need him to hit a good streak.
"We have been the kind of team, when he wasn't on a streak, there was somebody else who would step up and score goals for us. It's good to see Fredy get goals now."