Josh Lopez led off the bottom of the ninth with a home run, his second of the contest, in the opener of a doubleheader on Sunday against Chestnut Hill to send the Jefferson (24-19, 15-9 CACC) to the CACC Tournament.
Jefferson went on to win the second game, too.
The Rams secured the No. 3 seed in the South Division and now travel to Goldey-Beacom for a best-of-three series starting Friday.
The Griffins (20-23, 11-13 CACC) needed to sweep the Rams in the doubleheader to earn a postseason berth.
Chestnut Hill jumped ahead with a 5-0 lead in Game One before the Rams jumped on the scoreboard in the third.
The two clubs traded blows, with the Griffins evening things at 10-10 in the ninth when Connor Evans opened the frame with a single, stole second, and scampered home on a pair of throwing errors.
Lopez broke the tie in the bottom of the frame, launching the game-winning solo shot to left field. He finished the game 3-for-5 with two solo homers, while Justin Espinal was 3-for-4 with a homer. Arturo Figueroa led the Rams at the plate, hitting a pair of homers while driving in five runs.
Anthony Pillari recorded the win in relief, tossing two scoreless innings while collecting five strikeouts.
The Rams took care of things in Game Two, winning 21-7. Ryan Sawyer collected seven RBIs in the win while hitting three homeruns.