In 1642 a Cambodian Prince named Ponhea Chan became King Ramathipothei  after overthrowing and assassinating the previous King. Malay Muslim merchants in Cambodia helped him in his takeover, and he subsequently converted to Islam from Buddhism, changed his name to Ibrahim, and married a Malay woman. He then started a war to drive out the Dutch East India Company, by first starting a massacre in the capital of the Dutch, commandeering two of their ships, and killing 35 Dutch employees of the Company in addition to the Company's ambassador. On the Mekong River, the Cambodians defeated the Dutch East India Company in a mostly naval war from 1643-44 with the Cambodian forces suffering 1,000 dead, and the Dutch forces suffering 156 dead out of 432 soldiers and multiple Dutch warships fell into Cambodian hands. The Dutch East India Company ambassador who was killed along with his men was Pierre de Rogemortes, and it was not until two centuries later that European influence in Cambodia could recover from the defeat inflicted on the Dutch. This Muslim Cambodian King was ousted and arrested by the Vietnamese Nguyen lords after Ibrahim's brothers, who remained Buddhists, requested Vietnamese help to restore Buddhism to Cambodia by removing him from the throne. In the 1670s the Dutch left all the trading posts they had maintained in Cambodia after the massacre in 1643.
Answer this question: Which lost the battle on the Mekong River, Cambodians or Dutch East India Company?
Dutch East India Company