Marc Warren and Paul Dunne finished their first rounds with a flourish to lead the Open de Espana, while Jon Rahm and amateur Victor Pastor are just one shot off the pace in their homeland.
Warren, without a victory on the European Tour since 2014, birdied five of the last seven holes to start with a six-under 66 at Centro Nacional de Golf on Thursday.
The 37-year-old has failed to finish in the top 50 this year, but made just one bogey at the fourth and raised his game on the back nine to take over at the top of the leaderboard in Madrid.
Dunne matched Warren's opening round when he went out later in the day, the Irishman conjuring up an eagle at 18 after making three of his five birdies on the back nine.
Rahm arrived on home soil buoyed by a fourth-place finish in the Masters last weekend - his best showing in a major - and put himself firmly in contention to claim a first professional title in Spain.
The world number four hit the turn in 34 after starting on the back nine, an eagle three at 18 putting a spring in his step following his solitary dropped shot at the previous hole.
Rahm - who spent two years practicing on the course earlier in his career - made further gains at the third, fifth and seventh in a strong start to his challenge.
Pastor, 113th in the Amateur Golf Ranking, started with an eagle and came up with five birdies before a bogey at the last cost him a share of the lead.
Jason Norris, Jonathan Thomson, Julien Guerrier, Erik van Rooyen and Matthias Schwab are also just a solitary shot behind the leading duo on five under along with Alexander Bjork, Henric Sturehed, Callum Shinkwin and Aaron Rai.
Andrew Johnston, 2016 winner and defending champion as the tournament was not on the European Tour schedule last year, is among nine players a further stroke back.