PORTLAND, Ore. — Jack Sock needed a little time to get up to speed Friday in his first Davis Cup match. Once Sock got his serve straightened out, the U.S. raced to a 2-0 lead over Croatia in the best-of-five quarterfinal tie. Sock overcame a two-set deficit to beat Marin Cilic 4-6, 3-6, 6-3, 6-4,
