A third-round 71 at the Czech Masters saw halfway leader Jamie Donaldson slip two shots behind fellow Welshman Bradley Dredge, who fired a sparkling 66 on Saturday to move onto 12 under.
Kevin Phelan remains best of the Irish despite slipping back to two-under after a one over par 73.
Peter Lawrie (third-round 73) and Damien McGrane (74) are both one over.
Donaldson still has his Ryder Cup destiny in his own hands, but will have to work hard if he is to earn his place on the European team this weekend.
The Welshman can secure his spot at Gleneagles next month with a haul of just under €30,000 from the D+D REAL Czech Masters and next week's Italian Open.
He had appeared on course to ease his way through that barrier in Prague, where €166,660 euros is available to the man who ends the weekend at the top of the leaderboard, after leading following rounds one and two.
Donaldson could still make Paul McGinley's team via the world points list should he fail to enhance his bank account enough over the next nine days, but qualification via the European route would come as a relief, with Graeme McDowell, Ian Poulter, Luke Donald, Stephen Gallacher and Joost Luiten all battling to qualify via that route.
Missing the cut at The Barclays will have put a major dent in Poulter and Donald's chances of making the team that way, but McDowell is still very much alive in New Jersey with Gallacher and Luiten both in action in eastern Europe.
Gallacher sat four shots behind Dredge going into the final round after a 71, while Luiten was 10 behind after a 73.
Denmark's Soren Kjeldsen was just two shots adrift of Dredge after firing a 68 on Saturday but all eyes will be on Donaldson on Sunday.
"It was there for my taking today and to extend the lead," he said.
"I played well enough to do that but I didn't, too many sloppy mistakes but that's golf. I've played a lot of golf recently.
"I'm not too fatigued. I probably will be when it's finished but the adrenaline just keeps you going through the event if you're doing well. I'm not too bad now."
The 38-year-old threatened to run away with it when he eagled the first and picked up another shot on four to move him to 12 under, but he could not find consistency and a bogey on the next was followed by a run of birdie, double-bogey, birdie on seven, eight and nine.
Another birdie followed on 12 but bogeys on 13 and 18 meant he picked up just one shot on the day.
Dredge, by contrast, was faultless picking up birdies on five, nine, 11, 12, 14 and 15 to move him into the lead.
"I've had no bogeys since the first day and it's nice when you do that," he said. "All the birdies count then and I've been delighted with the last two rounds so if I can do that again tomorrow I would be over the moon.
"It's nice to be up the top and contending again at this tournament, it's what all of us guys practise for and I'm enjoying it so hopefully I can have a good round again tomorrow."
Frenchman Gregory Bourdy was three shots behind Dredge with South African Merrick Bremner alongside Gallacher on eight under. English pair Garrick Porteous and Paul Waring were alongside American David Lipsky a further shot back.