Peter Uihlein of the United States shot a second-round 68 to move into a one-shot lead at the halfway stage of the Spanish Open in Valencia.
The 23-year-old New Englander made three birdies in his last five holes to move a shot clear of a group of three players on five-under.
Sweden's Rikard Karlberg made bogey at the last two holes to drop out of the outright lead and is now a shot back, alongside Chilean Felipe Aguilar and France's Raphael Jacquelin.
Aguilar had 17 pars and a solitary birdie at the third in his 71, while Jacquelin shot a best-of-the-day 66.
Karlberg was five-under through his first four holes on the Parador de El Saler course after three birdies and an eagle two at the second.
He picked up further shots at 11 and 14 but dropped shots late in the day in a nervy finish to sign for a five-under 67.
The 27-year-old from Gothenburg may have become distracted by his lofty position at the top of the leaderboard; he has not had a top 10 finish all season and is down at No 174 in the Race to Dubai standings.
Aguilar, who has won more than 30 tournaments in his native Chile but just one, the 2008 Indonesia Open, on the European Tour, told European Tour Radio: "I played good."
"I had a bogey-free round with only one birdie and you could think it was a boring round, but it was quite exciting. I had a couple of bad shots and had to chip out and get up and down.
"Patience was key. I knew it wasn't going to be easy but I am quite comfortable playing right now. It's a long way to go and the weekend usually gets tougher. The greens are getting very hard."
Scottish pair Marc Warren and Craig Lee, England's Eddie Pepperell and Denmark's Andreas Harto and Morten Madsen are two shots off the lead on four under, with former Ryder Cup player David Howell among those a stroke further back.
Uihlein said: "It's nice to play a course like this now and then where distance isn't a premium and you have to think your way around.
"It's nice to play a course where a couple under par is a good score. I think courses that make you think are actually more fun.
"Leading a tournament is fun. I have been close a couple of times after two rounds, so it's nice to have the lead and be able to see how I do. It's all part of the learning process, and the more I do it the more comfortable I'll feel."