Jacquelin sank a 5-footer to finally overcome Kieffer in an epic playoff that equaled a European Tour record.
Jacquelin, Kieffer (1-under 71s) and Felipe Aguilar (70) began a three-way playoff after each finished at 5-under 283 following 72 holes at Parador de El Saler.
Aguilar was eliminated on the third playoff with a par while the other two competitors each logged a birdie.
Jacquelin missed potentially winning 15-foot birdie putts on each of the next three holes, allowing Kieffer to stay in it.
The marathon finally ended on ninth extra hole when Jacquelin put his approach within 5 feet and drained the birdie putt after Kieffer had misfired from more than 20 feet.
The long playoff battled equaled the previous European Tour record set at the 1989 KLM Open, when Jose Maria Olazabal outlasted Roger Chapman and Ronan Rafferty.
Third-round leader Mark Warren stumbled to a 4-over 76, ending in a tie for fourth place at minus-4 with Magnus Carlsson (71), Paul Waring (73) and David Horsey (73).