The Cardinals traded for John Lackey at the non-waiver deadline on July 31, and Neshek volunteered to change his number from 41 to 37. Lackey had worn 41 with past teams. To facilitate the exchange, Lackey mailed Neshek a Babe Ruth–autographed baseball the next month. In an August 10 appearance against the Orioles, Neshek's sinker was clocked at as he completed two innings and struck out four, tying a career high. On August 19 against the Cincinnati Reds, he worked the last inning and picked up the decision in a Cardinals' walk-off win. It was his sixth win of the year against zero losses. For the month, he registered two saves and two wins. In 2014 he was 7–2 with six saves and a 1.87 ERA, and 68 strikeouts in 67 innings. Despite having only given up 4 home runs the entire season, Neshek surrendered a postseason game-losing home run in Game 2 of the 2014 National League Division Series to Matt Kemp of the Los Angeles Dodgers and the game-tying home run in Game 5 of the 2014 National League Championship Series to Michael Morse of the San Francisco Giants, which ultimately led to the elimination of the Cardinals in the 2014 postseason.