Baltacha reached a career-high ranking of 49 in 2010 and won 11 singles titles during her career.
Del Potro stretched his Washington win streak to 14 matches by adding to the titles he won in the US capital in 2008 and 2009.
The unseeded Indo-German pair, which had shocked top seeds, lost 4-6 6-7(1) to the Filipino-Briton combo in the second round of the USD 1,295,790 hard court tournament.
They next face Treat Huey of Philippines and Briton Dominic Inglot in the quarter-finals.
Somdev, who created a record by retaining the NCAA title beating Isner 7-6 (7), 4-6, 7-6 (2) in 2007, was overpowered in their first meeting after that collegiate final here Thursday.
Somdev got the better of American Jesse Witten with a 7-5 6-0 scoreline. Sanam Singh had disappointment in store as he lost 0-6 5-7 to Australian 12th seed Samuel Groth.
The 12th-seeded Ivanovic faced a tough challenge from her French rival in the first set but raised her game in the tiebreaker.
Melanie Oudin of the United States has been awarded a Wimbledon wild card after reaching the final of the grass-court Aegon Classic.
Sixth seed Samantha Stosur of Australia reached the second round at the French Open on Sunday by defeating Britain's Elena Baltacha 6-4, 6-0.
Virginie Razzano and Pauline Parmentier won in contrasting ways to give France a 2-0 lead over Slovenia in their Fed Cup World Group II playoff on Saturday.
Japanese veteran Kimiko Date-Krumm and Vania King of the United States won their opening matches at the WTA Tour's Indian Wells tournament on Wednesday.
Andy Murray was the last Briton standing after a humiliating first day for the nation at the Australian Open on Monday when five players failed to win a single set.
Fifth-seeded Sabine Lisicki of Germany continued her roll through the Texas Open, going into the semifinals as the highest seed remaining and having yet to lose a set.
The top five seeds at the WTA San Diego Open sailed into the quarter-finals on Thursday, with only China's number four Peng Shuai taken to three-sets.
Top seeds Sania Mirza of India and Yaroslava Shvedova of Kazakhstan clinched the Citi Open women's doubles title, defeating second seeds Olga Govortsova of Belarus and Alla Kudryavtseva of Russia 6-3, 6-3.
Sania Mirza earned the opportunity to win her third WTA doubles title of the season as she and Yaroslava Shvedova breezed into final of the Citi Open after handing a humiliating 6-0 6-1 defeat to Shahar Peer and Sloan Stephens.