Jimenez, who turns 50 next month, rolled in an 18-foot putt to birdie the first extra hole to defend the title he won last year to become the tour's oldest winner.
Tied with burly Thai Prom Meesawat and Welshman Stuart Manley at 12-under after returning a final round 66, Jimenez drained a slick right-to-left putt down the slope to claim his 20th European Tour title.
"I love this place, I love this golf course, I love the tournament," Jimenez said after winning his fourth Hong Kong Open title.
Meesawat looked set for his maiden European Tour title as he eagled the third to grab the lead and went three clear with another at the long 13th.
He bogeyed the next, however, just when Jimenez was launching a late charge.
Overnight leader Manley had four bogeys and as many birdies in his first 10 holes before he joined the playoff with a brilliant chip-in for birdie at the last.