Upset in the acting category : yes or no

Has an actress with a good personal/professional reputation ever lost Best Actress after winning SAG, BAFTA, and the Globe? I don't think people love Judy, but I don't think they love any of the other performances enough to bridge the divide. If Scarlett or Saoirse won BAFTA, I'd be wondering more.

Not an actrESS but Russell Crowe in 2001 for A BEAUTIFUL MIND. People were expecting him to win his 2nd Oscar that year but he lost to Denzel.

I'm predicting Pitt but from what 8 read on the Oscar ballots interviews something makes me think he can get it based on sheer respect

Yeah, that's an interesting case.  But I think Crowe having just won and him being a bit of a prick at times makes the situation different, besides Denzel actually having the better and showier performance.  Crowe actually winning SAG felt like an afterglow thing, and Denzel films' release dates in the UK have always been weird BAFTA deadline-wise and part of why he's never been nominated there.  Zellwegger won many years ago, and doesn't have a hothead or diva reputation.  

If it happens anywhere it will be supporting actress.

Equating Crowe/Denzel to any of these races is such an incredibly dense false equivalency. Crowe had won the year before and basically tried to murder a BAFTA producer for cutting his speech short. Conversely, Denzel had a very public campaign and many high profile names were vouching for him (including the person who presented him the Oscar). The Academy was also under pressure for their historical lack of diversity. Plus, that season was so spread out that there was time for momentum to shift from the precursors. Three of the frontrunners are either due or overdue and the other simply has no competition. Any of the frontrunners losing would be, quite literally, the biggest upset of the century.

... Pitt literally has more votes than Pesci from these anonymous ballots. This place will never give up on The Irishman. It's like your lost puppy.

Pressed? No, I just find it hilarious this place's continued insistence than The Irishman is still in races that it has clearly been long out of it. Plus, your argument is absurd given the small sample of the premise it's based on isn't even true.

It's weird too considering how crazy well received it was when it came out, seemed like it was a serious Best Picture contender. The way films majorly pick up and then utterly lose steam during the awards race has always been kinda weird to me. 

Not happening.

Best Actress seems like the most likely place for an upset but I really highly doubt it’ll happen. All 4 seem pretty locked in.