Peterson, a left-hander who boasts an 11-1 record and 1.70 earned run average, will be pitching against the Shawnee Mission Slam at 8:15 p.m.
In the tourney opener at 6 p.m., the second-seeded Blue Valley Jaguars will tangle with No. 7 seed Mill Valley.
The Raiders (29-16) are the No. 3 seed. SM Slam (13-22) is No. 6.
On Wednesday night, the seven-team double-elimination tourney will continue with Olathe East against Paola at 6 p.m. followed by the losers of tonight's games at 8:15 p.m.
Top-seed Manhattan (31-13) will meet the Olathe East-Paola winner at 6 p.m. on Thursday with tonight's two winners scheduled in the 8:15 p.m. game.
So if the Raiders win tonight, they'll play at 8:15 p.m. on Thursday. If they lose, they'll play at 8:15 p.m. on Wednesday.
Losers bracket games are scheduled at 6 p.m. and 8:15 p.m. on Friday. The tourney will continue Saturday with games at 3 p.m., 5:30 p.m. and 8 p.m. The championship contest is set for 6 p.m. on Sunday with the winner earning a spot in the State Legion tournament next week in Newton.
"This really is a tough zone," Raiders coach Carl Brooks said. "There are three or four teams in this zone that ought to go to state. Out west, for example, there's a zone with only three teams."
Legion baseball is divided into seven zones with the host team always earning an automatic berth in the eight-team state tourney.
The Raiders' top two hitters are shortstop Matt Berner (.450) and catcher Troy Wingert (.404). Berner has 16 doubles and four home runs. Wingert shares the team lead in RBI with 39.
Another Raiders' player close to .400 is outfielder Rob Scott who has a .398 batting average.