Adair was signed by the Baltimore Orioles out of Oklahoma State University on September 2, 1958 for a $40,000 bonus. He made his Major League Baseball debut with the club that day against the Washington Senators, coming into the game in the bottom of the 8th inning as a defensive replacement for shortstop Chuck Oertel. He did not get an at bat in the game. Adair's first big league at bat came on September 5 against the Boston Red Sox. After drawing a walk and scoring in the 8th inning, Adair reached base again in the ninth inning on a fielder's choice. He picked up his first big league hit (a single to left field) in a 3–2 Orioles win over the visiting New York Yankees on September 21. That season, he hit .105 (2-for-19) in 11 games with the Orioles, primarily playing shortstop.