Question

how did Mark Antony outperform even a great orator like Brutus and turn the roman mob against him

Answer 1

he appealed to the emotions of the countrymen

Answer 2

Mark Antony knew the people of the country. he knew only if he lies the people will trust him and revolt against the conspirators. Whereas, Brutus was not as good as Mark Antony even though he could make the people understand that why they had killed Caesar
Mark Antony turns out to have a greater potential and a wide perspective of view.
He listens to Brutus's speech and mockingly calls the conspirators "honrable" the people being so trust worthy in Mark Antony Believes Him.