Celta were not finished in the first period, however, with Orellana notching his second with a curling effort after 39 minutes.
Betis improved in the second half, but Nolito's strike 15 minutes from time put Celta 4-1 ahead. Castro scored his second for Betis in the latter stages, but it was a case of too little too late for the Seville-based outfit.
Read how it all unfolded in Sports Mole's minute-by-minute live commentary of the action below.
CELTA: Yoel; Mallo, Costas, Fontas, Jonny; Oubina, Lopez; Krohn-Dehli, Rafinha, Orellana, Charles
BETIS: Sara; Juanfran, Amaya, Paulao, Nacho; Nono, Reyes; Baptistao, Verdu, Salva; Castro