He commanded the advance of the Greeks into western Central Greece the same year, and suffered a serious defeat at Peta on 16 July, but retrieved this disaster somewhat by his successful resistance to the First Siege of Missolonghi (Nov. 1822 to Jan. 1823). At Peta, Mavokordatos wanted a victory by his philhellene units and his Greek soldiers trained by the German philhellene Karl von Normann-Ehrenfels to show the advantages of professional military training to the Greeks. Mavorkordatos appointed Normann-Ehrenfels, formerly a captain in the Württemberg army his chief of staff. At the Argos assembly in 1823, Mavrokordhatos did not seek office again, but had himself appointed as general secretary of the Executive, which made him responsible for the flow of paperwork both to and from the Executive. In 1823, Mavokordatos supported the Senate in its dispute with the Executive dominated by supporters of his rival Theodoros Kolokotronis. In 1824, Mavrokordatos welcomed Lord Byron to Greece and tried to persuade him to lead an attack on Navpaktos. In 1824, Mavorokordhatos backed a plot by the American philhellene George Jarvis and the Scottish philhellene Thomas Fenton to murder his rival Odysseas Androutsos and Androutsos's brother-in-law Edward John Trelawny.