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.
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.
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.
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.
The top seeded pair of Sania Mirza and Yaroslava Shvedova stormed into the doubles semifinals of the USD 220,000 Citi Open after beating Lindsay Lee-Waters and Megan Moulton-Levy in straight sets.
Second-seeded Nadia Petrova of Russia defeated Canada's Eugenie Bouchard 6-2, 6-2 in 52 minutes to advance to the quarterfinals of the Citi Open.
Top-seeded Shahar Peer defeated Japanese qualifier Ryoko Duda 6-4, 6-2 to advance to the second round of the inaugural WTA Citi Open.
Virginie Razzano of France beat Japan's Misaki Doi 6-2, 6-2 on Monday night in the first round of the inaugural Citi Open just outside Washington, D.C.