Jimenez, 50 eagled his opening hole and then managed seven birdies in an 11-hole stretch starting on the fourth to fall one shot shy of equaling the Montgomerie Maxx Royal course record.
England's Ian Poulter, using a putter that helped him to a share of third place in last year's British Open, also recorded an eagle and seven birdies but a bogey left him one shot off the lead.
Three players — Australia's Wade Ormsby, England's Tyrrell Hatton and South Africa's Brendon De Jonge — share third on 7 under.
Eleven months ago, Jimenez broke his own record for oldest winner on the European Tour when successfully defending his Hong Kong Open title aged 49 years and 337 days.
This week also marks the Malaga-born golfer's 642nd European Tour event.
"To shoot nine-under par on this course in only first round, it's a good start," he said. "I was six under par after seven holes and playing very well, and you just try to enjoy yourself, and it's the way to shoot very low, still exciting and I managed to do that. ... So this is a special round because I've been struggling a little bit the last few months but when you shoot under par, you feel very good."
Poulter was also delighted with his effort after struggling in recent weeks and coming close to falling outside the top 50 in the rankings.
"I decided to switch back to my old putter late last week that has a softer insert and it felt really good on these quick greens," he said. "So the old putter is back in the bag. I also started to hit some good shots and I started to roll the putts in that I would expect to hole, and then it adds up to 8 under par."
Ormsby, competing in Turkey for a first time in his career, ended his round with six birdies in succession and played his inward nine in 7 under par that included eight birdies and a bogey on the 12th.
"I've had some hot runs the last few weeks including the Perth International where I had five birdies in a row and last week in the first when I played in India I had four in a row," said Ormsby. "But I'm just pleased to be here competing in an event of this stature".
American John Daly, competing on an invitation, shot a 3 under 67 while Scotland's Colin Montgomerie, celebrating his 600th European Tour event, signed for a 4 over 76.