Alex Lange limited top-seeded Oregon State to two hits over 7 1/3 innings, and LSU ended the Beavers' 23-game winning streak with a 3-1 victory Friday to set up a winner-take-all Bracket 1 final at the College World Series.
The teams will meet again Saturday, with the winner going to the best-of-three finals beginning Monday.
The Tigers (51-18), who avenged a 13-1 loss to the Beavers (56-5) on Monday, became the first team to knock off the Beavers since Southern California on April 29.
They scored all three of their runs against national wins leader Jake Thompson (14-1). Lange (10-5) retired eight in a row before he turned the game over to closer Zack Hess with one out in the eighth. Hess retired the last five batters, four by strikeout, for his fourth save.
LSU led 2-0 on Beau Jordan's safety-squeeze bunt scored Zach Watson in the second, and Josh Smith homered leading off the seventh.