Valderrama continued to bare its teeth on Saturday, but little-known Mike Lorenzo-Vera managed to escape most of the carnage.
The Frenchman posted a level-par 71 – one of the best scores an another punishing day at the Open de Espana – to finish on one over par after three rounds.
Incredibly, that was good enough for a one-shot lead over England's Andrew Johnson, who shot a 74, Germany's two-time major champion Martin Kaymer, who also managed to salvage a level-par 71, and Joost Luiten, whose 70 was one of only two under-par rounds on Saturday.
The tournament now looks likely to produce an over-par winner for the first time in Europe since the 2013 Open Championship.
Lorenzo-Vera is ranked just 312th in the world, but even though he found plenty of trouble during his third round, including a double-bogey seven at the fourth and three bogeys over his closing four holes, he also managed three birdies and an unlikely eagle at the 17th to ensure his battle with Valderrama at least ended in a stalemate.
The eagle at 17 was undoubtedly the highlight of the day, and came after Lorenzo-Vero holed his approach to the par-5. It sparked wild celebrations, and though he would bogey the 18th immediately after, it was still good enough to earn him a one-shot cushion heading into Sunday's final round, and a chance at a maiden European Tour title.
"I'm very excited," said the 31-year-old. "I'm going to have a big nap tonight because it takes so much energy to stay patient here.
"I'm just going to try to relax and enjoy it as much as I can tomorrow.
"I'm just trying to look at the pace of the leadeboard and accept that you're going to have a lot of bogeys here. A bogey on the hole is never really a bad score so you just try to accept it. Take the bogey and get out of there."
Kaymer, meanwhile, mixed four birdies with four bogeys, and is probably now the favourite heading into Sunday, as he looks to add to his tally of 11 European Tour wins.
Also still in with a shot are the likes of James Morrison and Ross Fisher at three over par, and Spaniard Pablo Larrazabal, who led overnight but slumped to a 78. He remains just three strokes back, however.
The exhibition match, against Phil Mickelson and Tom Brady, raised 20 million dollars.
The Dutchman finished third and second in the first two weeks of the home-based competition.
NFL stars Tom Brady and Peyton Manning will also be involved.
The US President was among the viewers watching the TaylorMade Driving Relief.
The US President phoned in as McIlroy played in a Sunday fundraiser for coronavirus victims.
Syme donated his prize money to charity.
‘This is the life of a caddie…’
The Northern Irishman is ranked number one in the world.
Players entering the United States will face a 14-day quarantine period, while a strict testing regime will be in place at each tournament.
The experienced duo will be involved at Whistling Straits.