Jack Sock has booked his place in the quarter-finals of the Swiss Indoors championship by beating John Isner in straight sets.
The world number 27, who has now overcome six top-15 players this calendar year, prevailed 7-6(5) 6-3 in Basel.
Both players held throughout a tight opening set, but it was the American who came out on top 7-5 in the tie-break.
Sock held once more in the second set while breaking his opponent in the eighth game to secure a straightforward passage into the final eight, where he will meet Donald Young.
