Upvote:3
By the letter of the rules, I don't think you stand any chance. You have been in the US for 90 days already, and exiting to Mexico does not reset the clock, so you will be trying to re-enter on the 91st day, which is clearly against the rules and the very definition of a visa run.
Now, you do have an onward flight, so if the CBP officer is feeling generous he might let you in anyway. But this sounds unlikely and really risky, and if he says "no", you're going to have a big immediate problem -- how will you get into the US for your flight? -- and a long-term problem as well, since if you're denied entry for any reason, you will now have to apply for visas every time you want to visit the US.
I can see two alternatives: