I'm very confused by what you mean. When you say "acquire power," are you talking about some particular event? Or are you just talking about their general influence? As politicians both Caesar and Pompey held various magistracies and levels of influence throughout their career, I'm really not sure precisely what you're asking about.

EDIT: What I'm getting at is that I can think of several points during each man's career that you could say he "acquired power." The establishment of the triumvirate is the obvious one (although in that case why rule out Crassus, who was decidedly senior in the arrangement to Caesar?) but even after the triumvirate it's not as though the triumvirs held the state solely in their grasp--Caesar barely fended off efforts to prosecute him for several years, and Pompey was constantly skirmishing with the likes of Publius Clodius and others, unable to eliminate them. And what do we do about things like the establishment of Pompey's extraordinary magistrate against the pirates and his war in the east, which left him undeniably the most powerful individual in the Roman state? Yet for all that Pompey's influence quickly receded in 61 an 60 with the failure of his repeated efforts to force through his Eastern Settlement and land distributions. So what are we defining as "acquiring power?" Are you asking about some sort of formal arrangement of magistracies and political powers? In which case we could point to both of their various consulships and magistracies. Or are you asking about influence, which is harder to pin down precisely but easily more important? "Power" is a pretty vague concept, as is its acquisition, especially with regards to the politics of the late Republican state, which generally prevented the acquisition of either enormous and pre-eminent legal powers or influence by any single individual for prolonged periods of time--until the end of the civil war this is as true for Caesar and Pompey as for anyone else.