Lim Song Chong, who suspected his girlfriend was in a relationship with her 65-year-old landlord Cheong Yee Mun, threw a kitchen knife at him in a brawl on holy ground.
He hurled the 20 cm-long knife at Cheong, who escaped being hit by hiding behind a pillar at the Glad Tidings Church.
Lim also threw an umbrella, a pocket knife and kitchen scissors at the landlord, who retaliated by chucking a fire extinguisher at his "very, very frail" rival, The Straits Times reported.
Lim was fined 3,000 dollars and jailed for a day after he admitted committing criminal intimidation by chasing Cheong with the knife and performing a rash act by throwing it at him.