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, 6-4, and John Isner topped Borna Coric 6-4, 6-4, 6-3 in the second match on the Tualatin Hills hard court.
The U.S. can wrap up the Davis Cup tie Saturday with a win in the doubles match between twins Bob and Mike Bryan and Ivan Dodig and Marin Draganja. Two reverse singles matches are scheduled for Sunday.
"Our mindset is we're happy," U.S. captain Jim Courier said. "For us, it's about putting our hard hats on and let Bob and Mike do what they do. I like our chances."
The U.S-Croatia winner will advance to the semifinals in September to face the Czech Republic-France winner. The United States is seeking its first semifinals appearance since 2012.
The United States is 157-3 when leading 2-0 in Davis Cup competition. The last time the U.S. blew a 2-0 advantage was the 1994 semifinals against Sweden.
The Bryan twins are 10-4 in Davis Cup doubles competition.
The 23-year-old Sock set the tone Friday, though it took a while to get going. Cilic, No. 12 in the world, rushed to a two-set lead after breaking Sock three times in the second set. But Sock also had his moments during the first two sets, and he used that, along with a bit of inspiration from Courier, to fuel a comeback.
"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.
Courier noted that Cilic might be struggling a bit mentally after the 27-year-old Croatian blew a two-set lead to Roger Federer in the Wimbledon quarterfinals less than two weeks ago.
"I was using that as a little bit of a carrot to keep Jack in there," Courier said.
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.
Isner dominated with his big serve in his three-set win over the 19-year-old Coric, getting 23 aces to Coric's three. The 31-year-old Isner, No. 16 in the world and playing in his 20th career Davis Cup match, broke Coric once in each set.
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.
The United States is trying to break a nine-year Davis Cup title drought. The U.S. won in 2007 when it beat Russia 4-1 in Portland. Croatia claimed its only Davis Cup title in 2005.
The U.S. has won a Davis Cup-high 32 titles, but only one since 1995.
In other quarterfinal ties:
• Britain 1, Serbia 1: Dusan Lajovic breezed past James Ward 6-1, 6-3, 6-2 to even up their tie at one match apiece in Belgrade, Serbia.
Lojovic won 10 straight points in breaking Ward at love and holding at love for a decisive 3-1 lead in the third set.
Britain took a 1-0 lead when Kyle Edmund beat Janko Tipsarevic 6-3, 6-4, 6-0 in the opening singles.
• France 1, Czech Republic 1: Lucas Pouille made a victorious Cup debut for France by beating Jiri Vesely 7-6 (2), 6-4, 7-5 to level Friday's matches in Trinec, Czech Republic.
Amid increased security following the deadly attack in the French city of Nice, Lukas Rosol saved two match points to prevail over Jo-Wilfried Tsonga 6-4, 3-6, 4-6, 7-6 (8), 6-4 in the first match.
A minute of silence was observed at Werk Arena before the opening singles to honor the 84 people killed by a truck in Nice.
"All my thoughts are with the victims and families of this tragedy," Tsonga tweeted.
• Argentina 1, Italy 0: Federico Delbonis won the first point for Argentina against Italy before weather postponed the second match between Fabio Fognini and Argentina's Juan Monaco until Saturday.
Rain overnight and through the morning delayed the start of the tie for 2½ hours, then Delbonis took more than 3½ hours to beat Andreas Seppi 7-6 (4), 3-6, 6-3, 7-6 (3) in Pesaro, Italy.