Sylvester Urban "Blix" Donnelly (January 21, 1914 – June 20, 1976) was an American professional baseball right-handed pitcher. Donnelly appeared in 190 Major League Baseball (MLB) games between 1944 and 1951 for the St. Louis Cardinals, Philadelphia Phillies and Boston Braves. In all, he had an 18-year (1935–52) professional career. Donnelly stood 5 feet 10 inches (1.78 m) tall and weighed 166 pounds (75 kg).