American Jack Sock reaches fourth round of US Open for first time

— -- NEW YORK -- Jack Sock, a 23-year-old American, is through to the second week of the US Open for the first time.

The No. 26 seed surprised No. 7 Marin Cilic with an emphatic 6-4, 6-3, 6-3 victory Friday to advance to the fourth round. Cilic won the 2014 US Open, his only major victory.

The big-serving Croatian came in as the hottest player in tennis, winner of eight straight matches and 14 of 15. Part of that run included winning the ATP Masters 1000 title in Cincinnati two weeks ago, beating Andy Murray in the final.

It was Sock's first win over a top-10 player in a Grand Slam, and it came in a swift 1 hour, 41 minutes. His only previous trip to the second week of a Grand Slam tournament came when he got to the fourth round of the 2015 French Open.

Sock is now 3-16 against top-10 players -- but 2-0 against Cilic, going back to July's Davis Cup win in Portland, Oregon.

"He can play some of the best tennis in the world," Sock said of Cilic in his on-court interview. "I took a lot of stuff from that match in Portland. I was down two sets to one, changed up the tactics.

"Feels great. It was a big match for me."

The Associated Press contributed to this report.