TALLADEGA, Ala.—Denny Hamlin is already through to the third round of NASCAR’s playoffs with nothing to worry about at Talladega Superspeedway. His championship rivals? Not so much. NASCAR’s challenging second round of the playoffs—three wildly different circuits—moves Sunday to the behemoth 2.66-mile Alabama superspeedway where luck is as important as skill. The white-knuckled race falls between Las Vegas, a traditional 1.5-mile speedway where Hamlin won last week, and the twists and turns of the hybrid oval/road course at Charlotte Motor Speedway next week. The unpredictability expected this week and next has the 11 drivers vying for seven remaining playoff slots slightly on edge. “You can’t freak out and try any harder because I’m already trying as hard as I can,” said Alex Bowman, who narrowly raced his way through to the second round only for Las Vegas to drop him right back to 11th out of 12 in the standings. …