Knight gave up a three-run home run to Kevin Seker in the top of the first inning as the Rebels fell behind for the first time 3-0.
Back-to-back doubles by Adrian Adams and Tim Jacobson and a run-scoring single by Knight gave the Rebels a 4-3 edge after one inning.
Marriotts Ridge (17-6) scored three more runs on a bases-loaded double by Mitchell Smith, but once again the South bats showed up to back Knight, who even pitched in and helped.
Tim Hamilton started things with a solo home run and Jacobson and Knight each added RBI singles. Three more runs scored on a pair of wild pitches and an error before Tyler Presgraves capped the eight-run frame with a two-run home run -- his eighth of the year -- to give the Rebels a 12-6 lead.
"This was big, huge. We came through," the sophomore Presgraves said. "(Knight) started out slow, but I had faith in him as a senior. He's been here a lot longer than I have."
Knight issued three bases-loaded walks in the third as the Mustangs cut the gap to 12-9.
"That was very uncharacteristic of our pitcher. We were very close to pulling him," said South coach Ralph Stottlemyer. "He was trying to pitch the corners when he just needed to pitch the game."
Knight labored through 100 pitches -- only 41 strikes -- through the roughest three-inning stretch of his career. But in a matter of minutes between the third and fourth innings, he turned it into his most memorable games.
He retired 12 of the last 15 batters he faced -- his only costly mistake was a solo home run to Seker in the sixth -- to send the Rebels (18-3) to the state championship game.
What changed? He simply moved from the right of the rubber to the center.
"I knew once it got later (in the game) that I would have to pitch better. I had to figure it out," he said. "I got stronger as the game went on, but I just couldn't find my location. This is the biggest win for me."
Knight polished the complete game with his 10th strikeout on his 156th pitch of the game. He allowed four hits and walked 12.
South tacked on two insurance runs after back-to-back singles by Tim Leather and Adams in the fifth. The Rebels finished with 13 hits and eight starters scored at least one run.
Leather finished with three hits, while Pregraves, Adams, Jacobson and Knight each added two.
"This was just a gutsy performance by our hitters," Stottlemyer said. "I don't care who the other team puts on the mound, we're going to hit the ball."
The Rebels will play Kent Island on Saturday at 4:30 p.m. at Ripken Stadium in Aberdeen, Md. Leather is slated to pitch the game but Knight said he will be ready in a relief role.