Youzhny lost only 11 points in nine service games while taking a 6-1, 6-4 decision over Rajeev Ram. He dominated the first set, winning three-quarters of the points and losing three points on serve.
Seventh-seeded Guillermo Garcia-Lopez earned the right to face Youzhny in Friday's quarterfinals. Garcia-Lopez had just finished off his fourth break of the day and was up 6-1, 3-1 when Paolo Lorenzi retired from the match.
Third-seeded Martin Klizan didn't face a break point in his 6-3, 6-3 decision over Simone Bolelli. His next opponent will be Ricardas Berankis, who won the first set 6-3 before No. 8-seeded Jurgen Zopp retired.
No. 4-seeded Fabio Fognini got by Sergiy Stakhovsky 7-6 (7-4), 6-4 in a 2-hour match. Also Thursday, Roberto Bautista-Agut topped Teymuraz Gabashvili 6-3, 6-4; Flavio Cipolla got by Grega Zemlja 6-2, 6-7 (5-7), 6-3; and Daniel Gimeno-Traver took out Lukasz Kubot 6-4, 7-6 (7-5).
The quarterfinals in the lower half of the draw have Fognini taking on Bautista-Agut and Cipolla playing Gimeno-Traver.
Swim Week Miami Beach 2014 [PHOTOS]