Ferrer, No. 3 in the world rankings, suffered two breaks in the first set before rallying for a 4-6, 6-3, 6-1 win over Jack Sock. Ferrer saw -- and saved -- the only three break points after the first set. Those came in the third set when he was only 14 points in the set.
Ferrer ended up winning more than two-thirds of the points on serve and a healthy 41 percent off Sock's serve.
No. 2-seeded Milos Raonic capped second-round play with a 6-2, 7-6 (7-3) victory over Joachim Johansson. Raonic had 16 aces while losing 12 points in his 10 games serving. He didn't face a break point.
Kenny De Schepper knocked off fourth-seeded Kevin Anderson 7-6 (7-5), 4-6, 6-3. Anderson faced only five break points and lost one. But that was the difference in the third set as De Schepper turned back both of Anderson's break chances in the set.
No. 5-seeded Ernests Gulbis had nine aces in a 6-3, 7-6 (7-3) defeat of Igor Sijsling and seventh-seeded Grigor Dimitrov rolled by Jan-Lennard Struff 6-1, 6-3 in 61 minutes. Also Thursday, Fernando Verdasco beat Jarkko Nieminen 6-2, 3-6 6-3.
Ferrer and Verdasco are paired against each other for Friday as are Gulbis and third-seeded Jerzy Janowicz. Raonic takes on No. 6-seeded Benoit Paire and Dimitrov plays De Schepper in the other quarterfinals Friday.