Sania and Tecau, who were seeded sixth, went down 5-7, 3-6 to the 10th seeded pair of Briton Jamie Murray and his Australian partner Casey Dellacqua in the third round of mixed doubles.
Paes and Stepanek registered a hard fought win over Nenad Zimonjic and Daniel Nestor in the quarter-finals.
The fifth-seeded Indo-Czech pair won 3-6, 7-6 (5), 6-3, 6-4 against the third seeded Serbian-Canadian pair in an encounter that lasted a gruelling two hours and 37 minutes on court 1. Paes and Stepanek looked rusty in the first set as Zimonjic and Nestor easily took the set in 33 minutes.
Paes had won the men's doubles title at Wimbledon in 1999
The Indo-Czech pair came back strongly in the second set and took it to the tie-breakers that they won 7-5. Nestor served well in the second set hitting five aces but also made four double faults.
In the last two sets, Paes and Stepanek found their rhythm and completely dominated the proceedings to carve out a tough win.
In the semi-final, Paes and Stepanek will face theA Canadian-American pair of Vasek Pospisil and Jack Sock, who pulled of a stunning 6-4, 3-6, 7-6, 6-4 against the second seeded Austrian-Brazilian combine of Alexander Peya and Bruno Soares.
Paes has won the men's doubles title at Wimbledon only once, in 1999. But he has three-mixed doubles titles here in 1999, 2003 and 2010. Paes is also one of the few to win both the men's doubles and the mixed doubles title together here in 1999.