Before the "Air Coryell" offenses of the mid-1970s captivated the football world, the trench work in St. Louis was anchored by a quiet, unheralded draft steal out of Illinois. Selected in the 13th round (176th overall) of the 1961 NFL Draft, Ernie McMillan arrived at training camp as a converted college tight end. The Cardinals quickly shifted his 6-foot-5, 275-pound frame to offensive tackle, unleashing a cerebral, technically sound blocker who would anchor the edge for fourteen consecutive seasons (1961–1974).

The mechanics of his play relied heavily on leverage, geometry, and exceptional lateral balance. In an era where pass protection was a hand-to-hand brawl against legendary edge rushers, McMillan excelled through calculated body control and precise angles. He was a textbook technician who mastered the art of mirroring pass rushers, once grading out at a staggering 96 percent efficiency on pass blocks across a single season. His endurance was equally remarkable; after taking over as the full-time starter in his second year, he set a franchise record by starting 162 consecutive games without missing a single contest due to injury over his first twelve seasons.

In a testament to his selflessness and leadership, McMillan willingly moved from his longtime right tackle slot to left tackle late in his St. Louis tenure to accommodate the rise of young star Dan Dierdorf. That positional sacrifice allowed the Cardinals to field one of the most formidable tackle tandems in league history. After a final 1974 season in St. Louis where he helped secure a division title, he finished his career with a brief stint in Green Bay in 1975, retiring with 190 career regular-season games.