He wasn't, there was another guy using BM in that battle: Nial Declann
"You must have wondered how a few dozen Rebel ships could possibly rout an Imperial force that outgunned it by at least ten to one… The Rebels did indeed fight better, but not because of any special abilities or training. They fought better than the fleet because the Emperor was dead… you must have noticed it. The sudden loss of coordination between crew members and ships; the loss of efficiency and discipline. The loss, in short, of that elusive quality we call fighting spirit… You had no real fighting spirit of your own anymore—none of you in the Imperial fleet did. It was the Emperor's will that drove you; the Emperor's mind that provided you with strength and resolve and efficiency. You were as dependent on that presence as if you were all borg-implanted into a combat computer."
―Thrawn to Pellaeon
The Emperor it had long been rumored had the ability to use the force to exercise direct control over his military forces. If the Jedi Master Luke had confronted on Jomark had the same ability
pg 21. The Last Command.
There are a few others in Heir to the Empire where he makes more direct mentions, DMB quoted one of them but I think there are like two more.
Originally posted by Nephthys
He wasn't, there was another guy using BM in that battle: Nial Declann
As he had maintained all along, Shimrra's death, recently reported by Kenth Hamner, had had no discernable effect on the enemy commanders or pilots. At the climactic battle of the Galactic Civil War, Imperial forces appeared to have been thrown into disarray by the death of Emperor Palpatine. But Shimrra was scarcely a Sith Master, capable of using his powers of battle meditation to invigorate his troops.
--The Unifying Force
I'm not sure if Declann was made after TUF or not, but there's another Palps BM quote I found.