The 35-year-old scattered three birdies and gave just one shot back, pooling a 34-34 card when the other big guns floundered, for a 281 total, five-under after four hectic rounds and a two-shot lead over Cassius Casas.
Casas, one-up on Ruben Sasutil and two ahead of Lascuna at the start of the day, wrestled with a wild driver all round, accounting for six bogeys against a birdie and the only eagle of the day to drop to solo second two shots adrift.
Lascuna, the reigning The Country Club champion, was hitting iron shots close, but the putting still has not worked the way he wants it in this P5 million, island-hopping tournament.
He missed a two-footer for par for his only bogey, which came at the 182-yard par-3 eighth, and also flubbed at least six more birdie chances no longer than 12 feet.
Benjie Magada made the loudest noise under overcast skies, shooting up from 18th spot to a tie for third after seven birdies and a bogey for a 64. The 38-year-old father of five now has a 284 total and is just three back going into the crucial fifth round at Del Monte.
Carito Villaroman rebounded from a 75 at Fairways in Boracay, turning in a 69 to move to that tie for third, even as Sasutil also had six bogeys in a 74 to drop out of second and be in solo fifth, four behind.
Though the fairways were soft, weird bounces were aplenty, and Casas failed to solve it. He did not hit a single fairway with his driver as all his bogeys resulted from playing out of the tree-lined roughs.
"There are still 36 holes to play and no one is assured of a win even with a big lead considering this format," Casas said in Filipino. "We will be going on another long trip today, and it’s hard to say that one player will be ready for the next round."
The players will have to endure another 12-hour overnight journey by sea aboard a Super Ferry to go to Cagayan de Oro, which will be their base for the last 36 holes starting today.
Tough Del Monte, a majestic par-72 layout designed by the revered Celestino Tugot, could pose as the last obstacle as it hosts the penultimate 18.
Only four players broke par yesterday and the same number failed to break 80. Richard Sinfuego assembled a 69 and joined Mars Pucay (74) and Robert Pactolerin (72) in fifth spot at 288, two-over after 72 holes.
Danny Zarate turned in a level 70 and is tied for sixth with Edwin Estrera (73) at 289, even as veteran Elmer Salvador also scrambled to score a 70 and be at 291 like Ramil Bisera (72) for joint seventh.