Scotland's Richie Ramsay dug deep to preserve a two stroke advantage going into the closing 36 holes of the Andalucía Masters at Club de Golf Valderrama.
But the 28 year old may well have to fight off the challenge of back-to-form Sergio Garcia if he is to land his second European Tour title.
Having started with a brilliant 65, Ramsay is now five under par after a two-birdie, three-bogey 72.
Driving into the rough cost him a shot on the 454 yard 18th, but France's Grégory Havret - runner-up to Graeme McDowell in last year's US Open Championship - bogeyed the hole too to reach halfway on three under.
Garcia, winner of his home Castelló Masters by a stunning 11-stroke margin last Sunday, is one further back after a second successive 70 on a lay-out where he has been a runner-up three times. No Spaniard has won a European Tour event at Valderrama.
"Going up against one of your idols on a course, this is a dream situation," Ramsay said.
“I look forward to playing with Sergio, his natural ability and the way he plays golf is the way that I like to play golf. He likes to shape it and move it, and use some imagination - he’s probably the best person doing that in the game.
“And also he connects to people, they like to go and watch him and he’s entertaining to watch. The guys out here appreciate how good he is and enjoy the fact that he’s back and playing well. I think we all want him to win a Major, but I hope he gives me a chance here!
“It was a really tough day and I hung in there. It just illustrates how good my six under round was.
"I hit so many fairways and so many greens, but couldn't get the ball to drop. But at the end of the day, my ball-striking was good and I've got to take the positives out of it."
Ramsay bogeyed the third and sixth, the two short holes on the outward half, but birdied the eighth and 11th.
Havret had a seven on his card for the second day running. After double-bogeying the long fourth in his opening 68 he lost his drive at the 547 yard 11th.
Birdies at the next two repaired the damage and after his 71 he commented: "This course does not accept any errors. Every hole is a real challenge and you have to focus on every shot.
“It’s a good round - we had the full wind today so it’s a test,” said Havret.
“It’s a little bit of a shame that I bogeyed the last but it’s still a good round."
Garcia needs to win again to qualify for next week's World Golf Championships-HSBC Champions in Shanghai.
"I could have been a little bit more aggressive with a couple of putts coming in, but my short game is pretty good right now," he said.
"It was difficult to hit fairways and to choose the right club. Thank God it’s soft because, if not, this would be Hell. But I’ve always enjoyed hard courses. Back-to-back wins would be a great thing, but I don’t want to get ahead of myself.
"Valderrama can catch you any time - you can never think that you have this course under control. Even without wind it’s asking you to hit all the shots in the bag.
"That’s the beauty of if. A course doesn’t need to be long to be tough."
Playing with Garcia, England's Justin Rose started each half with two birdies, but a hat-trick of bogeys from the 15th has left him one over.
Compatriot Ross Fisher was second overnight, but after a 67 he dropped to four over with a 79.
Thomas Björn is another on one over, though, and not out of the running for a fourth victory of the season yet.