Yarosz defeated former world welter and middleweight champion Lou Brouillard on May 7, 1937 in a ten-round points decision before 2,438 in Boston. With a darting left and a lightning fast right cross, Yarosz gained a large enough margin on points to take the decision. Brouillard offered strong opposition through the entire bout taking at least two rounds with strong body blows to Yarosz's middle, but his crouching southpaw defense was penetrated too often to even the scoring. In the tenth, Brouillard opened with a strong two fisted attack that had Yarosz retreating, but was knocked down for a count of two with a right before the round ended.