Newport Harbor, CdM and Costa Mesa are in wild-card games in their respective divisions today at 3:15 p.m.
The Sailors (16-10) are in Division I and play host to Roosevelt from Corona (12-12-1).
The Sea Kings (11-16) travel to San Bernardino to play Cajon (17-8) in Division III.
The Mustangs (14-13) are at home against La Cañada (14-9) in Division IV.
The Eagles and Lightning are each at home in first-round games set for Friday at 3:15 p.m.
Estancia (17-10) is in Division IV and plays Colony (16-9), which is from Ontario.
Sage Hill (17-5) plays the winner of today's Division VI wild-card game between Calvary Chapel of Moreno Valley and Victor Valley Christian of Victorville.
While the postseason is unfamiliar territory for Newport Harbor, its first-year coach, Patrick Murphy, is used to coaching during this time of the year.
Murphy has only missed the playoffs three times in his 14 seasons as a head coach or assistant. Under Murphy, the Sailors improved seven games in the win column from last season and they moved up one spot in the ultra-competitive Sunset League, taking third place.
Senior Blake Davey leads the Sailors with a .414 batting average and sophomore Matt Carpenter has a team-best eight home runs and 29 runs batted in.
Newport Harbor faces Roosevelt, an at-large entry from the Big VIII League. Roosevelt enters the playoffs having lost three of four games, a span in which it has only scored six runs.
Newport Harbor was in a rut down the stretch until it broke out of it in the regular-season finale last week. The Sailors earned their first playoff berth in 20 years with a 6-1 Sunset League upset of Edison, ranked No. 4 in the final Division I coaches' poll.
CdM clinched its postseason berth last week as well.