From 1088, Tzachas used his base at Smyrna to wage war against the Byzantines. Employing Christian craftsmen, he built a fleet, with which he captured Phocaea and the eastern Aegean islands of Lesbos (except for the fortress of Methymna), Samos, Chios and Rhodes. A Byzantine fleet under Niketas Kastamonites was sent against him, but Tzachas defeated it in battle. Some modern scholars have speculated that his activities during this time may have been in conjunction, and perhaps even coordination, with two contemporary Byzantine rebels, Rhapsomates in Cyprus, and Karykes in Crete.

In 1090/91, the Byzantines under Constantine Dalassenos recovered Chios. Undeterred, Tzachas rebuilt his forces, and resumed his attacks. In 1092, Dalassenos and the new megas doux, John Doukas, were sent against Tzachas, and attacked the fortress of Mytilene on Lesbos. Tzachas resisted for three months, but finally had to negotiate a surrender of the fortress. During his return to Smyrna, Dalassenos attacked the Turkish fleet, which was almost destroyed.