A knuckleballer specialist, Papai was one of 29 players to pitch for both St. Louis clubs. In his only major league full-season he went 4–11 with a 5.06 ERA for the helpless Browns. In parts of four seasons, he posted a 9–14 record with a 5.37 ERA in 88 appearances, including 18 stars, eight complete games, four saves, 70 strikeouts, 138 walks, and 239+2⁄3 innings of work.
Papai also enjoyed a brilliant minor league career as the pitching staff ace for the Houston Buffaloes of the Texas League, posting 20-win seasons for them (1947, 1951–53). He went 21–10, with a 2.45 ERA for the 1947 Dixie Series Champion Buffs and 23–9, with a 2.44 ERA for the 1951 Texas League kings. He also pitched in the Venezuelan Winter League during the 1951–52 and 1952–53 seasons, compiling a 15–16 mark with a 2.25 ERA in 47 appearances.