The victory marked the Quakers' first win in the NCAA Tournament since 1990.
Wyatt Henseler finished 2-for-6 and drove in the contest's first run in the fourth with an RBI double to score Appel after he reached earlier in the frame via a leadoff single. The Tigers answered with a pair in the sixth to take the lead before Appel delivered his two-run blow in the eighth.
Auburn clawed back with a run of their own in the eighth as Carson Ozmer issued a bases-loaded walk to the first batter he faced to force in the tying run, but he worked out of the jam to get the final out of the frame while keeping the game even.
Ozmer went on to pitch an outstanding 3 1/3 frames for the Quakers while allowing just one hit. He issued just the one walk and whiffed three to earn the victory.
Jarrett Pokrovsky worked a one-out walk in the 11th before scoring on a Ryan Taylor double to left center field to plate the winning run. The Quakers then bunted three consecutive times and manufactured two more runs for insurance.
Ivy League Pitcher of the Year Ryan Dromboski pitched well for the Quakers, tossing 5 1/3 innings while surrendering two runs. He walked four, but struck out eight.
Appel led the Quakers at the plate with three hits.
Penn will face Samford on Saturday night, with the winner advancing to the regional championship round on Sunday. The Bulldogs beat Southern Miss earlier on Friday in extras, 4-2.
Samford punched its ticket to the NCAA Tournament by winning the Southern Conference Tournament last week. After splitting their first two games in the tournament, the Bulldogs pulled off an extremely rare feat by winning three games on Saturday to win the tournament title. Samford started the day with a 9-5 win over UNC Greensboro, which sent the Bulldogs to the championship round where they would have to defeat Wofford twice. Samford then earned a 7-2 win over the Terriers to force a winner-take-all championship game. In that final game, Samford picked up a 5-2 win over Wofford for the tournament championship.
This marks Samford's fourth trip to the NCAA Tournament.
Auburn and Southern Miss will play an elimination game on Saturday afternoon.
