Pearson said he carried a lot of emotion into the Octagon after months of baiting from the Australian on The Ultimate Fighter: The Smashes.
"This fight's been a long time in the making; we started filming in June," Pearson said. "I went back to San Diego and prepared.
"I was just patient, and I knew the shots I wanted to land. I said all along I just need to touch him - and not be the bull like I normally am. I had to pick my shots and make him miss and see what opened."
He decked Sotiropoulos in each round with the fight stopped at 41 seconds in the third after a hard right.
Sotiropoulos executed a takedown towards the end of the first, but Pearson was saved by the bell.
Australian Robert Whittaker won the welterweight final over England's Brad Scott after the judges gave the fight to him 29-28 29-28 29-28.
Despite losing out on the UFC contract, Scott impressed in what turned out to be a war.
The lightweight final went to Norman Parke 30-27 30-27 29-28 over Colin Fletcher, with the former making good use of his wrestling skills.
Elsewhere, Hector Lombard took a first UFC win with a first-round stoppage of Rousimar Palhares then said he wants to face Michael Bisping.
Middleweight contender Michael Bisping has gotten under the skin of the former champion Judoka.
“I saw Hector Lombard in the elevator yesterday and I thought someone was playing a practical joke,” Bisping said at the UFC 149 Fan Club Q&A in July.
“It was like, who is this little poison dwarf? I’m like c’mon, seriously? Seriously? This is the guy with all the hype? I think he’s in the wrong weight class; there’s a 125 weight class he should be in though.”
Lombard said he would step in if Vitor Belfort got injured prior to his UFC fight with Bisping in Sao Paulo on January 19.
“I will jump in right away. I would jump in, in January. Let’s see what the UFC and their owners are planning. It’s up to the UFC, but I would really like to make that fight happen.”
Chad Mendes def. Yaotzin Meza (KO, round one)
Joey Beltran def. Igor Pokrajac (unanimous decision)
Mike Pierce def. Seth Baczynski (unanimous decision)
Ben Alloway def. Manuel Rodriguez (KO, round one)
Mike Wilkinson def. Brendan Loughnane (unanimous decision)
Cody Donovan def. Nick Penner (KO, round one)