The 51-year-old Spaniard performed a celebratory jig of delight after using a six-iron to ace the par-three eighth hole at Real Club de Golf El Prat.
Jimenez, however, could only manage a one-under-par 71 that left him six strokes behind Frenchman Edouard Espana who led the way after a 69 gave him a seven-under total of 137.
"I'm leading an Open with my name everywhere so it's pretty cool," Espana told reporters. "My family is from Spain, I like the country and my Spanish cousins are here this week."
Argentina's Ricardo Gonzalez (69) was one stroke off the pace while South African Darren Fichardt (73) and Michael Hoey of Britain (68) shared third position on 139.
World number seven Sergio Garcia, the highest-ranked player in the field, was on 147 after carding a 72.
(Writing by Tony Jimenez, editing by Ken Ferris)
