Robredo beat John Isner 6-7 6-3 7-6 after Sanchez saw off American Melanie Oudin 6-4 6-4.
The 10th seed will next play Alla Kudryavtseva after the Russian defeated American Melanie Oudin 2-6 7-5 7-5.
She will be replaced by Vania King, with Melanie Oudin, Liezel Huber and Alexa Glatch competing the team.
Varvara Lepchenko, Madison Keys, Sloane Stephens, Bethanie Mattek-Sands, Vania King and Melanie Oudin all advanced to the second round without losing a set.
Ivanovic's sixth-seeded compatriot Jankovic, who last year topped the women's rankings despite never having won a Grand Slam tournament, was upset by American qualifier Melanie Oudin.
With a 2-0 lead overnight, world No. 11 Flavia Pennetta's 7-5 6-2 victory over Melanie Oudin in Sunday's opening singles match gave the Italians an unassailable lead.
Teenage star Melanie Oudin continued her heroics with a second singles victory as she beat Julie Coin 7-6 6-4 to give her side an unassailable 3-0 lead.
Bethanie Mattek-Sands defeated Alize Cornet 7-6 (9-7) 7-5 for her first singles win in the women's teams tournament, while Melanie Oudin beat debutant Pauline Parmentier 6-4 6-4 in the second rubber.
With both the Williams sisters ruled out through injury, Melanie Oudin opened the tie for the hosts with a 6-3 6-3 win over Alla Kudryavtseva -- who was making her Fed Cup debut.
Seventh seed Vera Zvonareva defeated ninth seed Alona Bondarenko 6-2 6-1, 13th seed Melanie Oudin beat Christina Mchale 6-4 6-0, and eighth seed Daniela Hantuchova battled past Angelique Kerber 6-7 (6-8) 7-5 6-3.
应用推荐