Roger Federer has never lost a single match to any of the remaining players in the ATP World Tour Finals 2017.
Jack Sock is the first American to reach the semi-finals of the ATP World Tour Finals event since Andy Roddick in 2007.
Jack Sock, the American number one, came from nowhere to reach the ATP World Tour Finals, reaching London by winning the Paris Masters.
Roger Federer hasn't triumphed at the season-ending Tour Finals since 2011.
The 16th seed ended his Serbian opponent's fairytale run in the French capital to break into the world's top 10 for the first time and take the last place for London from Spaniard Pablo Carreno Busta.
American tennis player Jack Sock, ranked 18 in the world, took to Twitter to find the young fan from whom the towel was snatched.
John Isner entered the semi-finals of Paris Masters with a 7-6 (8/6), 4-6, 6-4 win over compatriot Jack Sock
Juan Monaco defeated Jack Sock in three sets to win the US Men's Clay Court Championships.
Jack Sock knocks out top-seed John Isner, to face Juan Monaco in final of ATP Houston open.
John Isner set up a quarter-final with compatriot Jack Sock after he entered the quarter-finals of the ATP Houston Open.
Jack Sock defeated Matthew Barton to advance to the quarter-finals of the ATP tournament in Texas.
Roberto Bautista Agut won the ATP Auckland Classic Title after Jack Sock was forced to withdraw early from the final due to flu.
Rafael Nadal hit 10 less winners than Jack Sock's 29 but was the more consistent of the two. He committed 10 less unforced errors than his opponent's 35.
Here's a list of players who can break out and make a name for themselves during the US Open 2015 tournament.
Jack Sock, who he youngest American man to reach the French Open last-16 since Pete Sampras 22 years ago, was at the bedside of his brother Eric who had been diagnosed with Lemierre's Syndrome at the start of this year.
Five-time champion Roger Federer defied 32-degree heat and crushing humidity to reach the US Open last 16 Saturday as potential semi-final rival Andy Murray almost wilted in the New York sweatshop.
John McEnroe made a brief return to play an exhibition doubles match on the opening night of the SAP Open, teaming with young American Jack Sock to beat Gael Monfils and Steve Johnson 6-4, 6-4 in a lighthearted match on Monday.
Andy Roddick, the 2003 champion, reached the third round of the U.S. Open by beating American teenager Jack Sock 6-3, 6-3, 6-4 on Friday.