本命（ほんめい）と対抗馬（たいこうば）が競り合（せりあ）ったお陰（かげ）で、ダークホースの彼（かれ）が漁夫の利（ぎょふのり）を得（え）たってわけだ。

Since the favorite and his rival were running against each other a dark horse like him was able to pull out in front.