John Isner felt the ball hit the line, so he conceded the point. It turned into a big moment for Jack Sock.

The seventh-seeded Sock advanced to the semifinals of the Hall of Fame Tennis Championships with a 6-4, 7-6 (4) victory over No. 1 seed Isner on Friday in Newport, R.I.

Next up for the 21-year-old Sock is third-seeded Lleyton Hewitt, who eliminated American Steve Johnson with a 6-4, 6-4 victory. It's the first career ATP Tour semifinal for Sock, who paired with Canadian Vasek Pospisil to win the doubles title at Wimbledon.

Sock and Hewitt will play today after induction ceremonies honoring the 2014 class into the International Tennis Hall of Fame, which is highlighted by Lindsay Davenport in the recent player category.

Sock and Isner were tied at 1 in the second-set tiebreaker when Sock hit a serve and paused to look at the chair umpire when it was called out. Isner conceded the point. Sock won the next point and never trailed again, winning the final three points of the match.

Sock had conceded a point down 30-0 in the third game of the set.

Isner was certain he did the right thing.

"I thought it hit the line," he said. "I thought I saw the ball hit chalk. The ball is in, the ball is in."

Sock won the match when Isner hit a backhand return long.

The other semifinal is second-seeded Ivo Karlovic of Croatia against Samuel Groth of Australia, who won their quarterfinal matches on Thursday.

- The Associated Press