Syndergaard started in Game 2 of the 2015 National League Division Series against the Los Angeles Dodgers. He picked up the loss in that game as the Dodgers won 5–2, but he only allowed three runs in innings pitched with nine strikeouts and four walks. On October 15, he made his first Major League relief appearance in Game 5 . He pitched a scoreless seventh inning in that game, helping the Mets secure the victory and advance to the 2015 National League Championship Series (NLCS). He started Game 2 of the NLCS and picked up the victory, giving up three hits, one run, and one walk while striking out nine in innings pitched. The Mets swept the Cubs in four games and won the National League pennant, their first since 2000.