Hockey League. He played 36 games with Providence during the 1940–41 season, scoring 33 points, before being reassigned to the Kansas City Americans of the American Hockey Association, whom Chicago had just purchased as an additional minor-league affiliate. He finished the AHA season with 4 points in 7 games. The Black Hawks first recalled Mosienko in 1942, replacing players who had left to fight World War II. He scored his first two NHL goals on February 9, 1942, 21 seconds apart. An ankle injury kept him out for several weeks, and he finished the season with 14 points in 12 NHL games. Mosineko returned to Winnipeg for the summer of 1942 and worked in a defence plant. He tried to enlist in the military but was refused for medical reasons, likely related to his small size. He was also unable to cross into the United States as a result of travel restrictions and played the 1942–43 season primarily with the Quebec Aces of the Quebec Senior Hockey League, appearing in 8 games for them and scoring 5 points. He appeared in two games when the Hawks traveled to Toronto. He finally established himself as an NHL regular in 1943–44 and scored a career high 70 points. Mosienko and his linemates Clint Smith and Doug Bentley combined to score 219 points, at that time an NHL record. His 70 points set a team rookie record that stood for 37 years until broken by Denis Savard in 1980–81. In 1944–45, Mosienko finished sixth in league scoring with 54 points and did not record a single penalty minute throughout the course of the season. He was awarded the Lady Byng Memorial Trophy as the NHL's most gentlemanly player and named a second-team All-Star. He was also voted the most popular player on the team by its fans. The following season, Chicago coach Johnny Gottselig paired Mosienko with the Bentley brothers: Max and Doug. The trio formed what came to be known as the "Pony Line" due to their speed and small size and emerged as one of the top scoring trios in the NHL. Max Bentley led the league in scoring in 1945–46, and despite missing time with a knee injury, Mosienko finished sixth. He was again named a second-team All-Star. He played in the first National Hockey League All-Star Game prior to the start of the 1947–48 season, during which he suffered