Nipper pitched for the Red Sox from to . He was included with the league's top players in the ballot for Rookie of the Year in . But then a succession of injuries limited his success. He started 26 games for the 1986 Red Sox, posting a mediocre 10–12 win–loss record and 5.38 earned run average as Boston won the American League East Division title. He did not appear in the ALCS against the California Angels, but made two appearances on the mound for the Red Sox in the 1986 World Series against the New York Mets. Nipper started Game 4 on October 22 at Fenway Park and held the Mets scoreless through three innings, but in the fourth, he surrendered three runs, two on a home run by Gary Carter. Nipper righted himself after that inning and pitched through the sixth, but the three runs he allowed held up as the winning margin in a 6–2 New York victory. Then, in the winner-take-all Game 7 at Shea Stadium October 27, Nipper was called upon in relief as Boston's fifth pitcher of the contest. Entering in the eighth inning with the Mets leading 6–5, Nipper was ineffective. He retired only one batter and allowed three hits, including a lead-off home run to Darryl Strawberry and a run-scoring single to opposing pitcher Jesse Orosco, enabling the Mets to pad their lead to an insurmountable 8–5; they won the world championship one inning later.