China Southern Airlines has Los Angeles to Singapore at $346.63 round trip through Expedia.com for flight departures in April and May 2018. These are one-stop flights via Guangzhou. Most itineraries do not force an overnight, although that is an option for some dates.
Ticket prices show as $381 on Google Flights fare calendar for many dates in April, but Expedia offers an even lower ticket price with a $34 discount, reducing the ticket price to $347 round trip.
China Southern Airlines
LAX – Guangzhou CAN – Singapore SIN – CAN – LAX
Expedia.com ticket price