One of 20 Spaniards in the field this week, the three-time DP World Tour sustained an injury while making a midnight trip for a glass of water while in the United States last week but was determined to tee it up in his national open on Thursday.
Twice a winner already this season, Chacarra carded a five-under-par 66 that contained two eagles as he was later joined at the summit of the leaderboard by Scottish duo Connor Syme and Grant Forrest.
"It's been tough," he said. "I don't know what's going to happen tomorrow, but obviously I need to take care of myself.
"Obviously, I had a good round, but just how I feel physically, it's not great. I don’t know, it’s just hard. It’s a struggle.
"It doesn’t really hurt when I’m swinging. That’s the only good thing. It’s why I can still make a score, but it’s just been really tough to walk.
"I made it through today but the pain I had [over] the last holes walking is something that I don’t know if it’s worth it because I’ve got a lot to play for in the next couple of weeks.
"So, I’ll just sit down with the team and see what we decide because it was tough."
Daniel Hillier, who made his first DP World Tour hole-in-one at the 17th to win a BMW iX5, is in a four-strong group one shot further back alongside Spanish pair Angel Ayora and Sergio Garcia and Denmark's Jacob Skov Olesen.
Hillier mixed five birdies with three bogeys in addition to his ace in his 67, Ayora was five under on the par fives alone, Garcia delighted the home crowds too, while Skov Olesen was bogey-free.
Joe Dean and Mikael Lindberg, both winners this season, are among seven players a shot further back at three under.