On a day of unforgiving bloodletting for Rory McIlroy and Tiger Woods , it was the infamously indifferent, slow-playing scourge of JB Holmes who soared to the top of the leaderboard on a rain-drenched opening day at Royal Portrush.After flurries of thick downpours and gusting winds wreaked lunchtime havoc over the Dunluce Links, the unfancied American took advantage of a late blaze of afternoon sunshine and sodden greens to play his way into a clubhouse lead with methodical precision, carding just a single bogey on the opening hole.A somewhat unpopular character with supporters due to a lethargic routine that can double for anaesthetic, Holmes had missed the cut in three of his last four major coming into the tournament, but was undeterred as he tapped into a vein of power-walking form to take a one-shot lead over Shane Lowry. The Irishman too benefiting by way of the weather after his dawn start skirted the impending downpour and afforded him a cosy afternoon in the clubhouse.From extras.For hours it appeared that Jon Rahm was primed to become the day's runaway leader. After storming to victory across the border in Lahinch less than a fortnight ago, he blistered to an unmatched five-under-par front-nine. But as his temper blew with irregular bluster to rival the weather, the short-fused Spaniard lost his spark on the 14th hole when a fatted approach had him stamping and seething at the ground below. Dressed in a padded jacket bearing an uncanny resemblance to a bulletproof vest, the 24-year-old, who previously employed a bomb-disposal expert in a bid to aid his anger, could only quell an explosion with heavy gulps after dragging the resulting par-putt wide of the hole. Another bogey on the 18th left him undeservedly disconsolate and marred what had otherwise been the day’s purest display of ball-striking.He joins a pack that features a remarkable 14 players two-shots off the lead, spearheaded by Brooks Koepka who started in familiarly looming form on his chase for a major victory, carding just a single birdie, despite bearing the brunt of the midday weather.