Baltacha moved to a career high world ranking of 62 on Monday
British number one Elena Baltacha has qualified for the first round of the Sony Ericsson Open, but her compatriot, Katie O'Brien, failed to progress.
World number 62 Baltacha advanced thanks to a 6-4 7-6 (8-6) win over Chan Yung-jan, of Chinese Taipei in Miami.
O'Brien, Britain's number two, slumped to a 6-4 6-2 defeat by Holland's Michaella Krajicek.
Baltacha joins fellow Brits Anne Keothavong and teenager Heather Watson, who got a wildcard, in the main draw.
Last week at Indian Wells in California, Baltacha negotiated the qualifying route, before eventually being ousted at the third-round stage by Australian Alicia Molik.
In the second round of that tournament, 26-year-old Baltacha had clinched her first win over a top-10 ranked player with victory over Li Na.
World number 138 Molik, meanwhile, also won through to the opening round in Miami with a 6-1 6-1 win over American Ashley Harkleroad.