PORTRUSH, Northern Ireland — Dustin Johnson called Tiger Woods over on the 6th green at Royal Portrush to check out his green-reading book.

“There’s, like, a million arrows!” he said. “They’re all touching each other. I can see ’em all — I just can’t see where they’re pointing.”

Woods cracked up.

But Johnson had a point — the treachery of links golf is back, and the undulating greens that come with it. On Monday morning, Johnson, Woods and Rickie Fowler — three tournament favorites — teed off at 8 a.m. local time for an 18-hole Open Championship practice round. Royal Portrush, a 131-year-old course on the tip of Northern Ireland, is hardly new, but few of the competitors have ever played here. That means study time.

Although Woods hasn’t teed it up since the U.S. Open a month ago, he’s had a busy schedule. From Pebble Beach, he headed to Southeast Asia for a 12-day trip with his mother Tida, his kids Sam and Charlie, and his girlfriend Erica Herman. The trip was reportedly the brainchild of Tida, who wanted her grandchildren to see where she had grown up, now that they’re old enough to appreciate it.

Post-vacation, Woods returned to Florida, where he’s been prepping from home (and practicing early wake-ups). On Saturday night, he packed up the jet for Portrush, landed Sunday morning and headed straight for the course. Woods has played mostly nine-hole practice rounds of late, but Portrush is particularly foreign — and demands particular attention. He and Patrick Reed trekked 18 and were done by early afternoon.