The 38-year-old returned six birdies and two bogeys in a four-under 68 to set the pace along with Challenge (second tier) Tour graduates Morten Madsen of Denmark and Frenchman Gary Stal.
Former Ryder Cup stalwart Miguel Angel Jimenez, competing for the first time since breaking his leg in a skiing accident in December, plunged to a four-over 76 while fellow Spaniard Sergio Garcia had to be content with a 72.
Aguilar made a good start to the season with three top-10 finishes but he decided to take a break from golf after his form nosedived.
"I took a couple of weeks off," the 2008 Indonesian Open champion told reporters. "I realised I needed some time off to relax.
"This course is playing very nicely especially in the morning with very little wind. It's a very difficult course if you miss the fairways off the tee so I'm quite happy with my 68."
Dane Madsen, from the same Silkeborg club as Players Committee chairman Thomas Bjorn, had five birdies and a solitary bogey at the El Saler course.
Stal was the only member of the leading trio not to drop a stroke to par.
One stroke off the pace on 69 were British trio Craig Lee, Matthew Southgate and Daniel Brooks, Swedes Joakim Lagergren and Joel Sjoholm, Ireland's David Higgins, Dutchman Robert-Jan Derksen and Spain's Gonzalo-Fernandez Castano.
- Sports & Recreation
- Morten Madsen
- Miguel Angel Jimenez
- Sergio Garcia