ATP World Tour Finals: Jack Sock beats Marin Cilic
The 25-year-old beat fifth seed Marin Cilic 5-7, 6-2, 7-6 (4) to move to 1-1 in Group Boris Becker.
The 25-year-old beat fifth seed Marin Cilic 5-7, 6-2, 7-6 (4) to move to 1-1 in Group Boris Becker.
Second-seed Federer, 36, needed one hour and 31 minutes to defeat the American debutant 6-4, 7-6 (4).
"I'm happy the way the day went" said Roland Garros and US Open champion Rafael Nadal.
Anderson seeks his fourth and biggest career ATP title on the Washington hardcourts.
The host nation now needs just one more win for a berth in the semifinals.
Federer, a four-time Indian Wells champion , will take on 17th-seeded American Jack Sock in the semis.
