Both payers drove into sand but recovered to give themselves a chance to make a birdie with sizeable putts on the 18th at San Diego's Torrey Pines course.
Westwood was first to putt and left his effort short, having to settle for third at the year's second major, while Woods holed his to force the play-off with his 45-year-old compatriot.
Woods and Westwood carded 73s on Sunday and, while Westwood can reflect on what might have been, Mediate will now be the underdog to claim his maiden major, with a resurgent Woods set to take him on over 18 holes in southern California.
Woods was ecstatic after seeing the ball roll around the cup before falling in, but Mediate confessed he always thought that the world number one would sink the putt when it really mattered.
"Unbelievable. I knew he'd make it," he said. "I will just have to get ready for a battle royale tomorrow (Monday).
Despite the size of the task ahead, Mediate is relishing the chance to put his wits against Woods on a one-on-one basis.
"How many opportunities does anyone have to go up against the best player on the planet in the US Open?" he added.



