Or Marcos does not win in 1965. Macapagal does - perhaps with Marcos staying in the Liberal party for the meantime. Marcos only achieves the presidency at a later period when Cold War politics and Philippine domestic politics makes it unlikely to achieve.
The late sixties and early seventies were the crazy years. If Marcos was President at a different time, it's less likely the Filipino establishment and the US would tolerate martial law, the level of corruption, etc.