I've always thought that was peculiar. I'm recalling this from my aging brain (at work again - no books!), but my general impression is: Octavian raises a volunteer army, perhaps as many as 8-10,000 men, and makes his first march on Rome in the fall of 44 BC, but it's a major dud - he gets no attention from the Senate and a lot of his men disband. Antony is preparing to fight up in northern Italy against Decimus Brutus' (legal) proconsular armies, which will eventually end up fighting him at Mutina. Octavian is deeply in the sh**. Two of the primary legions returning to Italy from Macedonia, literally at the last minute (Antony had gone, in November, to the Senate to denounce Octavian as a renegade and declare him 'hostis') end up switching from Antony to Octavian through internal mutinies, and the fact that Octavian was offering far higher bounties for soldiers than Antony was. In fact, at least one of Antony's legions had mutinied down in Brundisium and, to correct their demands for more money, he decimated them.

So in the end, the critical shift of legionary might in the end of 44 BC literally saved Octavian's bacon and gave him back credibility in the fight against Antony. It could have so easily gone the other way.

So why did the troops drop Antony, who after all was Caesar's liutenant and a well-known and popular commander, to go for this 18 year old kid who paid better but had nothing going for him but his name?

I've always felt that there were worlds of intrigue, including perhaps bribery, lots of secret meetings between Octavian's agents and the legions, etc., etc. that we will never know. When you think of it, it is an astonishing result.

I dug up the proper page on my Augustus site, which gives a slightly more coherent version of events in the fall of '44:

Octavianus