Guess there's several "right" answers, depending on what federation, what meet, witnesses, etc. I had posted somewhere that I thought Dave Waddington, complete with bloody nose, was the first to do it in the early 1980's, if you discount the anecdotes about Paul Anderson 20 or more yrs earlier, but this was at a local meet.
Lee Moran came later, BUT his was at the USPF Nationals, so you pay your money and take your choice on those two I guess. All this plus actual footage of the amazing story porky tells about Lee is in a vid I just stumbled into on youtube. I'll try to post a link, but I have bad luck with posting youtube links sometimes. Just in case, the way I found it was to key "powerlifting documentaries" into the youtube search. This one is 1 hr and 42 min long, dammit, and has the specific title "Power Unlimited." If you have any interest at all, I guarantee you'll like most or all of it. Starts with the pre-PL roots of powerlifting, explains how and why we got so many federations from what was once just the AAU, includes the only Mike Lambert footage I'd seen, on and off throughout the vid, debate of bench-only vs. all-3 meets, Mendy, Capt Kirk, Coan, many from the beginning up till a few yrs ago.
The part with Waddington and Moran runs roughly from 8:00 - 12:00