The 23-year-old Sock, playing in his first career home Davis Cup tie, won the fifth set after breaking Cilic to take a 5-4 lead on the Tualatin Hills hard court. Sock won the last four points of the final game, claiming the 3-hour, 13-minute match when Cilic hit his final shot into the net.Sock said the victory is a career highlight.“It’s up there for sure,” Sock said. “Haven’t played a ton of five-setters, haven’t come back from two-down. To do that in front of the home crowd, it feels really special.”In the second singles match Friday, the U.S.’s John Isner faced Borna Coric. The Davis Cup tie continues through the weekend, with a doubles match Saturday, and two reverse singles matches Sunday.Cilic, the 2014 U.S. Open champion and current world No. 12, was tough early on, breaking Sock’s serve late in the first two sets to take a 2-0 lead. Sock didn’t flinch.“I had a ton of chances in the second. I didn’t get blown off the court. I just had to make a few smarter decisions on the first serve and returning,” Sock said.The big-serving Sock bounced back, using an early service break to win the third set. Sock, No. 26 in the world, then pulled even, winning the fourth set by claiming the final two games.Cilic said it wasn’t momentum swinging in Sock’s favor as much as the young American simply improved his play.“Jack started to serve really well … he was not giving me too many chances in the return game,” Cilic said.The outset of the dramatic fifth set didn’t favor Sock, as he fell into a 3-0 hole. Having a veteran at his side in U.S. captain Jim Courier helped ease any doubts, Sock said.“I wasn’t very happy being down 3-0, but again, I just stayed the course. Jim just kept me levelheaded, to keep doing the right things. It paid off in the end,” Sock said.Sock came back by breaking Cilic in the fifth game, and eventually pulled even at 3-3. After each player held serve to keep the match tied at 4-4, Sock took control by breaking Cilic. The match-clinching game didn’t come easily for Sock, however, as he lost three of the first four points to Cilic.Cilic felt he didn’t let down as much as Sock surged.“Maybe I could have served better today. But he’s very dangerous. He can play very fast tennis,” Cilic said. “I didn’t play a bad match. I was fighting well.”The win over Cilic capped a big Friday for Sock, who earlier in the day was named to the U.S. Olympic team.“As a kid you grow up and it’s kind of on your bucket list. I’m very excited to get down there and hopefully play some good tennis,” Sock said.The U.S. last hosted a Davis Cup match in 2014, when it lost in the first round to Britain in San Diego. This is the fourth time Portland has hosted a Davis Cup tie.Croatia claimed its only Davis Cup title in 2005.