Manny Pacquiao has lost his WBO Welterweight title to a relative unknown in a shock defeat for the Philippines boxing hero.

Australian underdog Jeff Horn dispatched “Pacman” in an unanimous 12-round decision Sunday in a match dubbed the “Battle of Brisbane.”

“The Hornet,” a 29-year-old former schoolteacher, was considered an uneven match for veteran Pacquiao, who is considered one of the world’s greatest boxers.

Suncorp Stadium, packed with 50,000 people, erupted in cheers as Horn was declared the winner on points: 117-111, 115-113, 115-113.

However, it wasn’t long before social media shot back with allegations the judges got it wrong.

Three-time world heavyweight champion Lennox Lewis disputed the result on Twitter: “This is what’s wrong with boxing. Horn was very game but I’m hard pressed to see how he could have won that fight by any stretch!”

With the fight, Pacquiao’s career record falls to 59-7-2, while Horn now stands at 17-0-1 — on wins, losses and draws.

A tally by Compubox put Pacquiao ahead with 182 landed punches over Horn’s 92, though 73 of those were power punches, according to the stats.

Despite the outcry over the decision, Pacquiao was gracious in defeat.

“I didn’t expect [him to be] that tough,” he said after the fight. “It’s OK. Part of the game. That’s the decision of the judges. I respect that.”

Hall of Famer trainer, Freddie Roach, felt the 117-111 scorecard should be investigated.

“That was hard, sometimes I think people need to be investigated,” Roach told the Daily Telegraph. “At least in America where you get odd scores like that with the judges, the head commissioner should ask at some point, ‘Why? Where? Show me how you came up with that score.’”

“You have to think about [Mark Nelson] refereeing more fights or not, he’s maybe just not doing a good job. That is a WBO concern, I think they should do something about it, but I don’t think they ever will. The wrestling, getting hit behind the head a lot, it didn’t look good, but the referee didn’t pay any attention to it.

“I don’t know how he let a professional fighter get away with things like that, if you end up in a headlock after every exchange, someone is doing something wrong.”