The Bulldogs (50-18) need one win to reach next week's best-of-three finals. They're off until Friday, when they'll play Indiana (49-15) or Oregon State.
The Bulldogs erased a 3-2 deficit in the eighth. Brett Pirtle beat Will Nolden's throw home to tie it after DeMarcus Henderson smacked a one-out liner into right, and Porter sent Brian Korte's 3-1 pitch into the right-center gap to score Wea Rea and Henderson for a two-run lead.
Indiana got a run back in the ninth, but closer Jonathan Holder came on to get the last out in relief of Chad Girodo (9-1). Holder earned his 20th save.
Ryan Halstead (4-5) took the loss.
Oregon St. 11, Louisville 4
It's one down and three to go for Oregon State.
The No. 3 national seed Beavers stayed alive at the College World Series on Monday, beating Louisville 11-4 after a seven-run fourth inning broke open the game.
Oregon State won national championships the last two times it played in Omaha, in 2006 and '07, and coach Pat Casey's first title team did it the hard way.
The Beavers (51-12) face the same challenge as that 2006 team, having to win four straight after losing their CWS opener to reach the best-of-three finals. Next up is Indiana or Mississippi State on Wednesday.
Casey said he's careful not to compare this year's team to the 2006 squad, though the situation makes it seem unavoidable.
"They're all different clubs, they're different personnel," Casey said. "I think they've got a pretty good understanding of what it is they have to do. We talk about things that this team needs to do, and they usually respond."
The Pac-12 champion Beavers won conference series against Oregon and fellow CWS participant UCLA after losing the first games of series. In a super regional, they bounced back from a Game 1 loss to beat Kansas State.
Oregon State enjoyed a stress-free afternoon against the Cardinals (51-14), who committed four errors against the Beavers and 13 in their last six games.
Ben Wetzler (10-1) allowed three runs in 6 1-3 innings while Louisville starter Jeff Thompson (11-2) lasted 3 2-3 innings, with three of the seven runs against him unearned.
Oregon State scored the most runs allowed by Louisville this season. It was the highest-scoring game at the CWS in the three years it's been played at TD Ameritrade Park.
"It takes a little edge off the players if they can get a win in Omaha," Casey said. "No one on this club has ever won a game here. So I think it was good to see them relax a little bit."
Andy Peterson went 3 for 4 and Max Gordon had two hits and two RBIs out of the No. 9 hole for the Beavers.
Louisville scored just one run in two CWS. The Cards were 1-2 in their only other Omaha appearance, in 2007.
"We came here with the expectation to win the whole thing, and that's why it hurts," Cards coach Dan McDonnell said. "I told the guys one day we will win a national championship at Louisville. The '07 team got us on the map and we've been in regionals six of the last seven years. This team made a strong statement. I challenged them to leave their mark on Louisville baseball, and they did."
Oregon State capitalized on a hit batsman and two errors for a three-run third inning against Thompson, the Detroit Tigers' third-round draft pick.
Gordon was plunked leading off and scored from first when Tyler Smith doubled into the left-field corner.
Peterson's bunt single and a walk to Michael Conforto loaded the bases. Conforto should have been retired, but Louisville catcher Kyle Gibson dropped a high pop foul along the third-base line.
Two runs came home when Cardinals second baseman Zach Lucas, after fielding a slow grounder, made a careless flip wide of shortstop Sutton Whiting.
"Coach Casey has taught us little things always win the big games," Gordon said. "So we just come out and we played real aggressive on the defensive side and sacrifice our bodies if need be."
The Beavers all but finished off the Cards in the seven-run fourth, batting through their lineup for the 18th time this season and scoring all the runs with two outs.
Dylan Davis just beat third baseman Ty Young's throw on a bases-loaded chopper. Louisville first baseman Zak Wasserman, thinking Davis was out and the inning over, started jogging toward the dugout unaware that Peterson was coming around to score from second.
Two more runs scored on Whiting's overthrow of Wasserman, and reliever Kyle Funkhouser's bases-loaded walk and Gordon's single brought in three more.
The Cardinals ranked a respectable 76th out of 296 Division I teams in fielding after the regular season, but they committed two or more errors in five of their last six games.
"Overall I really didn't think Jeffrey pitched that bad," McDonnell said. "I would have liked to have seen us play better behind him, because he was competing. He was going to give us a chance."