style="background:#bfb" | 136 || September 2 || @ Braves || 2–1 (10) || Ron Reed (10–7) || Joey McLaughlin (4–3) || None || 10,040 || 68–67 |- style="background:#bfb" | 137 || September 3 (1) || @ Pirates || 2–0 || Steve Carlton (14–11) || Bert Blyleven (11–5) || Tug McGraw (14) || see 2nd game || 69–67 |- style="background:#fbb" | 138 || September 3 (2) || @ Pirates || 3–7 || Jim Rooker (3–6) || Randy Lerch (7–12) || Kent Tekulve (25) || 43,444 || 69–68 |- style="background:#bbb" | – || September 5 || Mets || colspan=6 | Postponed (rain); Makeup: September 6 as a traditional double-header |- style="background:#fbb" | 139 || September 6 (1) || Mets || 3–5 || Ed Glynn (1–2) || Nino Espinosa (13–11) || Andy Hassler (2) || see 2nd game || 69–69 |- style="background:#bfb" | 140 || September 6 (2) || Mets || 2–1 || Randy Lerch (8–12) || Pete Falcone (5–12) || Rawly Eastwick (5) || 21,091 || 70–69 |- style="background:#fbb" | 141 || September 7 || @ Cubs || 3–4 || Dennis Lamp (11–8) || Tug McGraw (3–3) || None || 10,359 || 70–70 |- style="background:#bfb" | 142 || September 8 || @ Cubs || 9–8 || Rawly Eastwick (3–4) || Bruce Sutter (4–5) || None || 20,767 || 71–70 |- style="background:#fbb" | 143 || September 9 || @ Cubs || 2–15 || Rick Reuschel (17–9) || Kevin Saucier (1–4) || None || 20,922 || 71–71 |- style="background:#bfb" | 144 || September 11 || @ Mets || 5–2 || Nino Espinosa (14–11) || Pete Falcone (5–13) || Rawly Eastwick (6) || 4,713 || 72–71 |- style="background:#bfb" | 145 || September 12 || @ Mets || 4–0 || Randy Lerch (9–12) || Craig Swan (12–12) || None || 4,158 || 73–71 |- style="background:#bfb" | 146 || September 13 || @ Mets || 2–1 || Steve Carlton (15–11) || Juan Berenguer (0–1) || Tug McGraw (15) || 3,890 || 74–71 |- style="background:#fbb" | 147 || September 14 || Cubs || 0–2 (10) || Bruce Sutter (5–6) || Ron Reed (10–8) || None || 20,838 || 74–72 |- style="background:#bfb" | 148 || September 15 || Cubs || 8–1 || Dan Larson (1–0) || Lynn McGlothen (11–13) || None || 33,042 || 75–72 |- style="background:#bfb" | 149 || September 16 || Cubs || 4–3 || Ron Reed (11–8) || Dick Tidrow (12–5) || None || 30,261 ||