ERA in 11 starts, striking out 40 and walking 14 in innings while completing seven games. He then was used as long reliever and spot starter in 1973, and went 4-5 with a 4.68 ERA in 39 games. Furthermore, he accomplished his only career shutout against the St. Louis Cardinals on April 28, limiting them to four hits and one walk, while striking out six in the 1–0 victory. Following a subpar season in 1974, Willoughby was traded to the Cardinals in exchange for second baseman Tom Heintzelman. Then St. Louis sent him to the Boston Red Sox in July 1975 to complete an earlier deal made for shortstop Mario Guerrero. Boston Red Sox By 1975, Boston was on the way to its first pennant since the 1967 "Impossible Dream" season, and Willoughby helped the team win the title when the bullpen was short handed and plagued by injuries of late. Willoughby had never been a full-time reliever before, but he responded with a very solid season, as he made 24 appearances and went 5-2 with eight saves and a 3.54 ERA in innings of work, but was not used in the 1975 ALCS against the three-time defending World Champion Oakland Athletics, which was swept by Boston in three games. Nevertheless, he assumed relief duties in three crucial games of the 1975 World Series against the Cincinnati Reds. In Game 3 of the Series, Willoughby relieved in the bottom of the seventh inning with the score tied at 5–5 and retired nine consecutive hitters. He returned in the bottom of the tenth inning, only to set the stage for a wild and controversial finish. Willoughby gave off a leadoff single to César Gerónimo. After that, Ed Armbrister attempted a sacrifice bunt that bounced high near the plate toward the first-base line. And Armbrister hesitated before running, apparently thinking the ball would go foul, while Boston catcher Carlton Fisk appeared to collide with him as he was retrieving the ball. In a controversial decision, the umpiring crew did not call Armbrister out for interference. Amid the confusion, Fisk attempted to force out Gerónimo, but his throw sailed high over shortstop Rick Burleson. This allowed Gerónimo to advance to third and Armbrister to advance to second. Both Fisk and Red Sox manager Darrell Johnson argued that Armbrister should have been ruled out for interference, but home plate umpire Larry Barnett ruled otherwise.