After spending the 1949 and 1950 seasons in the Braves' farm system, he made Boston's 1951 roster out of spring training. He pitched exclusively in relief through May 23, posting a 3.00 ERA. In his first starting assignment, June 3 at Braves Field against the Cincinnati Reds, he held a 2–1 lead into the eighth inning when Cincinnati rallied for three runs; Nichols was saddled with the 4–2 defeat, but he threw a complete game and earned a place in Boston's starting rotation.
He spent two seasons in the Braves' minor league system before making Boston's 1951 team out of spring training. He pitched exclusively in relief until May 23, posting a 3.00 ERA. In his first start, June 3 at Braves Field against the Cincinnati Reds, he held a 2–1 lead into the eighth inning when Cincinnati rallied for three runs; Nichols was saddled with the 4–2 defeat, but he threw a complete game and secured a spot in Boston's starting lineup.