MACAU, China - Boxing is a hurt business, as Manny Pacquiao found out when he ended up face down on the canvas after being knocked out just three fights ago by Juan Manuel Marquez.

It's also a risky business, and there are some in the sport who believe Pacquiao is taking a big one when he gets up Sunday morning in this gambling enclave for his welterweight title fight with Chris Algieri.

This is a fight he must not only win but look good while doing so if there is to be any hope of a megafight with Floyd Mayweather Jr.

"A fifth- or sixth-round knockout would be perfect," promoter Bob Arum said.

Pacquiao is a heavy favorite against Algieri, a New Yorker who seemingly came out of nowhere to get the fight. But Algieri poses problems for Pacquiao with both his height - he is a half head taller - and a left jab that he used to come back from two first-round knockdowns to beat hard-hitting Ruslan Provodnikov in his last bout. Algieri is unbeaten in 20 fights.

"When I look into the mirror I know I've done all the work necessary to win this fight," said Algieri, who holds a master's degree in clinical nutrition.

Pacquiao believes he has plenty left as he approaches his 36th birthday, and is eager to put on a show in a 13,000-seat arena that will include plenty of Filipino fans eager to see him show the punching power that turned him into a pay-per-view star.

Algieri, a former kickboxing champion who still lives in the basement of his parents' home on Long Island, has become somewhat of a sensation in the New York area after his win over Provodnikov in June. He would become much bigger should he overcome the 7-1 odds and beat a fighter who is a national hero in his own country.