Paul Broadhurst birdied two of his final three holes for a 1-under 69. He is tied for second place with Spain's Gonzalo Fernandez-Castano, who fired a 4-under 66, at minus-eight.
Markus Brier posted a 1-under 69 and is alone in fourth place at 6-under-par 204.
Emerson began the third round with a one-shot lead, but quickly extended the advantage. His sand wedge approach from 125 yards at the first took a few hops then fell into the cup for an eagle, which gave him a three-shot lead at minus-10.
The Englishman plodded along with pars until the par-4 sixth. His tee shot landed in the fairway, but he hit his second heavy and landed in rough near a greenside bunker. Emerson's ball embedded in the rough so he was able to place the ball, but came up short of the green with his third. He chipped his fourth to a foot and tapped in for a bogey.
Emerson still owned a two-shot lead, but that evaporated one hole later. His drive at the seventh landed in the trees on the right and forced him to pitch back into the fairway. Emerson's third landed in a greenside bunker, where he blasted out to 12 feet. He missed the bogey putt and fell to 7 under par thanks to the double-bogey.
Luckily for Emerson, all of his closest competitors were making mistakes in the rain as well. He still was on top of the leaderboard, but appeared to be in trouble at No. 9.
Emerson's drive at the ninth clipped a tree and fell only 150 yards from the tee box. His second landed in a bunker 55 yards from the putting surface and he blasted out to 10 feet. Emerson holed the clutch par putt to keep first place.
Fernandez-Castano matched Emerson in the lead at minus-7 after a birdie by the Spaniard at the 14th. At the par-5 12th, Emerson split the short grass with his tee ball, then knocked his second to 10 feet. He drained the eagle putt to go to 9-under par and reclaim his two-shot lead.
Emerson parred out his remaining holes.
'It is hard to keep on an even keel after a start like that and I had a sticky patch in the middle of the round, but I never felt it slipping away from me,' said Emerson, whose only tour victory came at last year's Russian Open. 'It's going to be a big day for me tomorrow, but I'm determined to take it one step at a time.'
Both Fernandez-Castano and Broadhurst trimmed the margin. Fernandez-Castano rolled in a 3-footer for birdie at the last to get within one, but Broadhurst had more work to get into second.
The Englishman birdied the 16th to get to 7 under par for the championship. At the par-4 17th, Broadhurst sank an 8-footer for birdie to go to 8 under par.
Broadhurst had a chance to tie Emerson at the last. His drive went well left of the fairway, but he had a playable lie. Broadhurst knocked his third 10 feet past the hole on the fringe, but missed the birdie try.
'It certainly was an up-and-down day for me,' admitted Broadhurst, who captured this year's Open de Portugal. 'But I knuckled down and battled back well because you are going to make bogeys out there, I don't care who you are, the way it was set up. Nobody was going away either so you just have to try and hang around.'
Maarten Lafeber, the 2003 winner, shot an even-par 70 and is tied for fifth place with Peter Senior (68) and Alessandro Tadini (71). The trio is knotted at 5-under-par 205.
Miguel Angel Martin and Andrew Oldcorn posted matching rounds of even-par 70 and are tied for eighth place at minus-4. Defending champion David Lynn (7) and Steven O'Hara (72) share 10th at 3-under-par 207.