Tournament host Tommy Fleetwood shrugged off the effects of a virus to move into contention to win his own event as a late stumble from Matt Wallace threw the destiny of the £3million British Masters wide open.
Wallace birdied the first three holes of round three to move four shots clear, but after going 47 holes without dropping a single shot he bogeyed the 12th and ran up a double bogey on the 15th after a wayward drive which hit a spectator on the head.
The 29-year-old Londoner, who is seeking a fifth European Tour title in just two years, steadied the ship with a birdie on the 17th and eventually signed for a 70 to share the lead with Sweden's Marcus Kinhult on 14 under par.
Scotland's Richie Ramsay is two shots off the pace after a 71, with compatriot Robert MacIntyre alongside Fleetwood on 11 under after both carded rounds of 68 in tough, breezy conditions at Hillside.
"Obviously I'm frustrated with dropping a couple on the 15th hole but I think I showed a little bit of character there to not let it affect me too much and I played the last three holes really nicely," Wallace said.
"I was trying to take a little note out of Tiger's (Woods) book and let them try to catch me but I hit two bad shots today and that's what happens in golf and I'm pretty happy with how I handled myself out there.
"I would have taken two under at the start of the day, seeing how windy it was. We are in great shape. It's not about winning it on Saturday. It's about putting yourself in good position, so looking forward to tomorrow now."
Fleetwood had followed his first birdie of the day on the eighth by dropping shots on the next two holes, but the Ryder Cup star then holed from 25 feet for an eagle on the 11th and also birdied the 12th, 14th and 17th to delight the sell-out crowd.
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"I've been a bit slow for two and a half days so it was great to get something going and give the crowds something to cheer," the Southport-born world number 16 said.
"I never realised how the last few holes are like a natural amphitheatre and playing in front of your home fans, especially when so many have turned out, it has exceeded expectations in every way.
"I've not had great energy levels. My son Frankie had tonsillitis last week and he's given me something, so that's not been ideal. It's one of them things, just another challenge.
"I forgot my paracetamol in the bag so Clare (his wife) had to get me some on the 13th tee and that pretty much saved me on the way in. Whatever happens I'm going to be going out late on the back nine on Sunday and the crowd comes to watch that, which is great."
Ramsay, who is seeking a first win for four years, recovered from a double bogey on the 10th with three birdies in the next six holes and was millimetres away from a hole-in-one on the 16th.
"I'm more than satisfied with the day because I thought it was tough out there," Ramsay said. "The wind seemed to pick up just as we were starting, it was quite strong and in a different direction today which was interesting.
"I'm pleased with the way I played. Had a little hiccup on 10 but bounced back on 11 and just played solid down the stretch.
"Obviously the tee shot on 16, that could have went in the hole but just went over the edge."