Starter Eric Walker (8-2) left the game after throwing four pitches in the third inning because of forearm tightness.
Chase Haney (3-2) worked two-thirds of an inning for the win, and Drew Carlton earned his seventh save after Fullerton put two runners on base with two outs in the bottom of the ninth. On the base paths, LSU was hurt by its own poor choices and by a missed call on the umpires.
In what we thought was going to be a close, tight game, top-seeded Oregon State turned it into a rout. "A heck of a way for a 17-game winning streak to end", coach Paul Mainieri said.
Oregon State took a 1-0 lead in the top of the first inning against Walker when center fielder Steven Kwan singled, moved to second on Madrigal's ground out and scored on a single by Larnach.
LSU's 17-game streak ranks as the fifth-longest this season.
In addition to Harrison's home run, offensively, Nick Madrigal led the Beaver attack with three hits and three RBI.
Madrigal tapped the ball back to freshman Todd Peterson, a play that should have at least resulted in a runner being thrown out at the plate.
Eight LSU pitchers walked 12 batters, a season-high and maybe the most in Mainieri's 11 seasons coaching the Tigers. Senior left-hander Jared Poche will start for LSU.
After the Beavers' early attack, LSU righthander Eric Walker settled into the game, retiring four straight batters.
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Fehmel struggled earlier in the season and actually was the losing pitcher in two of the Beavers' losses.
Oregon State broke the game open in the sixth with Harrison's grand slam. With one out and the bases loaded, Peterson fumbled a potential inning-ending 1-2-3 double play off the bat of Madrigal and was forced to settle for the out at first. He'd apparently experienced forearm soreness during a simulation game before the team left for Omaha, and his exit was an unwelcome loss for a team that suddenly needed to deal with an arm missing from the rotation. Creighton plays its home games at the park.
After the Beavers took a 8-0 lead in the sixth, however, they were a regular occurence. With the extended usage of sophomore Caleb Gilbert on Monday, Mainieri is without his first option in long relief. Every time we made a mistake, they took advantage of it. Nick Bush was having a hard time throwing strikes, so I brought in Hunter Newman trying to keep the game close.
On this very up night, he shushed the LSU masses, and there were lots of them. Gilbert then gave up a single to Madrigal, who took second base when Watson overthrew the cutoff man. Larnach followed with a two-run single. They will play Florida State on Wednesday, June 21 in Omaha.
With the game slipping away on a warm Monday evening, LSU opted to pitch around red-hot Trevor Larnach and load the bases for KJ Harrison.
The biggest hit of the day was a two-out grand slam by KJ Harrison that doubled Oregon State's lead in the sixth inning.
"The main thing, it helped me get my mind straight and give my arm a break", Fehmel said of his sabbatical.
The terror didn't end for LSU there, though, as Oregon State knocked in two more runs in the top of the eighth off of Austin Bain, the Tigers' seventh pitcher of the night.
"That's why all we've got to focus on is Wednesday's game against Florida State (which LSU beat 5-4 in the CWS opener Saturday)".