By this time, the only rival to Thonburi authority was the Sakwangburi lordship led by the powerful monk Chao Phra Faang. Chao Phra Faang’s domain encompassed the northernmost territories bordering Lanna to Nakhon Sawan to the south as the result of annexation of Phitsanulok lordship in 1768. In 1770, Chao Phra Faang sent reinforcements southwards reaching Chai Nat. Taksin perceived this action as threats and decided to invade Sakwangburi beforehand. The royal fleet marched upstream the Chao Phraya River and took Phitsanulok with ease. Taksin then divided the armies into the east one led by Boonma and the west one led by "Phraya" Pichai to be joined at Sakwangburi. Sakwangburi quickly fell after three days and Chao Phra Faang went lost.