Lahiri ceded the leadership to Swede Pelle Edberg, who followed his second round 62 with a 63 to move to 14-under, one shot ahead of Lahiri.
Lahiri, who has had just one bogey in 54 holes, had four birdies against no bogeys in the third round but was far from happy with his putting, needing no less than 34 putts for his round of 66.
Lahiri continued his progress in Girona but reiterated that there is no room for complacency with half the contest still to go.
"It has been good so far and I've hit it really well. Today was the best I've hit it all week, but probably the worst I have putted in three months. I hit it awesome, but had 34 putts to shoot 66, so that is half my round there. It is something I need to improve over the next two or three days, but the rest of the game feels good, so I've just got to keep that up," said the 27-year-old.
"I'm really happy, and I've played really good. I'm just trying to find as many greens as I can and take the pressure off myself, and I've done that well today. Obviously the next three days will be a sterner test on the Stadium course, and I really look forward to that," he added.