King Bayinnaung sent a massive invasion in 1568 in response to the uprising. In early 1569, the city of Ayutthaya was directly under threat and Vientiane sent reinforcements. The Burmese had planned on the reinforcements however and King Setthathirath fell into a trap. After a two-day struggle the Lan Xang forces prevailed at the Pa Sak Valley near Phetchabun, at which point one of the commanding generals from Nakhon Phanom broke south toward Ayutthaya. The Burmese rallied and were able to destroy the divided forces, and King Setthathirath had to retreat toward Vientiane.