Pacquiao's performance in the 118-110, 116-112, 116-112 unanimous-decision loss at the MGM Grand Hotel was marked by an ineffective right hand that zapped some of the expected fireworks from the faceoff between the world's top two boxers and drew criticism from many who put down $99 to watch the bout on pay-per-view.
The southpaw landed just 18 jabs to Mayweather's 67, and after planning a volume-punching effort, Pacquiao (57-6-2) threw six fewer punches than the defensive-minded Mayweather (48-0).
"Those numbers are crazy," Pacquiao promoter Bob Arum said. "Mayweather's a great fighter, and you can't beat him with one hand."
Pacquiao said "there's a tear" in the shoulder.
Pacquiao, according to training-camp insiders who spoke to The Times after the bout, suffered the injury about a month ago when he and a heavier sparring partner each threw simultaneous overhand rights and their arms collided, twisting Pacquiao's shoulder.
The pain was so troublesome that the thought of requesting a postponement to Pacquiao's long-awaited showdown with Mayweather was considered, they said.
Instead, according to one member of Pacquiao's camp who spoke on the condition of anonymity because the official wasn't authorized to discuss the health issue, said the fighter didn't want to subject fans and others to another delay after the bout had languished for more than five years.
"I thought the progress [before the fight] was good enough," Pacquiao trainer Freddie Roach said.
One camp insider said Pacquiao was confident the shoulder was feeling better, comfortable enough to say he could "test it" in the ring against Mayweather.
But in the third round, the pain returned, Pacquiao said.
Pacquiao said that even when he produced his best round in the fourth, backing up Mayweather with a hard left, "I felt the pain when I'd throw a punch or combinations."
Pacquiao said he devoted extensive time to developing his left-handed power punch after getting hurt in the closed training session not available to reporters, and that rest made his right shoulder feel better -- "but not 100 percent" -- one week before the bout.
Arum said his office on Monday had submitted a written request to the Nevada State Athletic Commission for Pacquiao to use an injection of three prescription medications, including the anesthetic Lidocaine, to help treat the fighter's possible discomfort with the shoulder.
"We assumed everything was OK," Arum said. But when a request for the medicine was made Saturday by Pacquiao's doctor, respected orthopedist Dr. Neal ElAttrache, it was rejected, the promoter said.
Commission Chairman Francisco Aguilar said his staff, contacted by an Arum staff member, wasn't asked until 6:08 p.m. Saturday if the injection could be used. Without proof of an injury, Aguilar said, the answer was no.
Aguilar noted that at Friday's weigh-in, Pacquiao's camp checked "no" in a form's box asking to confirm any injuries.
"[Roach and Pacquiao] felt the shoulder had sufficiently recovered, but you needed that shot for insurance," Arum said. "I think the commission, by turning its back, affected the outcome of the bout."
"This [training] camp, we had to postpone two weeks of it, because I couldn't use my right hand," Pacquiao said. "We planned to file with the commission an exception for numbing my shoulder, but we respect the opinion of the commission."
Arum said despite the $99 pay-per-view price tag on a bout that's expected to shatter boxing revenue records, he didn't regret, as one reporter put it, "staging a bout with an injured fighter."
"Athletes always fight hurt," he said. "We felt he had the opportunity to use the right hand. We were disappointed the injury kicked up in the third round, but this is always the case with sports. A guy is injured in training, deals with it, thinks he's conquered it, then gets reinjured in the game. Happens in every sport ... ."
Mayweather, now 48-0, treated the injury revelation as though it was sour grapes, saying he gets beat up in training too but wouldn't lean on an excuse if he had lost.
Pacquiao sought a bout with Mayweather for more than five years, but Arum said his fighter could now require surgery. At the same time, Mayweather said after the bout that he plans to fight just once more, in September, and then retire.
So Mayweather-Pacquiao looks like one-and-done.
"I didn't complain in the ring, it's part of the game," Pacquiao said. "I did my best, but my best wasn't good enough."