Allen was added to the Eastern Conference team Thursday by commissioner David Stern after Nelson was forced to pull out because of a torn labrum in his right shoulder. Allen joins teammates Paul Pierce and Kevin Garnett on the roster for the Feb. 15 game in Phoenix.
"He should have been on there, so it's nice," Celtics coach Doc Rivers said. "Having those three doing things together is nice, so I'm happy with the news."
Allen will be making his ninth All-Star appearance, having also been added as an injury replacement last season. He scored 28 points in New Orleans to help the East to a 134-128 victory over the West -- even outscoring game MVP LeBron James, who had 27.
"If injury replacement gets you 28 points in the All-Star game, I'll take it every year," Allen said. "I wasn't worried about it. But for three of us to represent the organization" is an honor.
Allen received a standing ovation from the Boston Garden crowd when the selection was announced during the first quarter of Thursday night's game against the Los Angeles Lakers. But the news drew jeers from the Cleveland Cavaliers, who believed Mo Williams should have been picked to give them multiple selections.
Cavaliers general manager Danny Ferry was disappointed Williams was bypassed.
"I know Commissioner Stern has followed our team's success, but maybe doesn't appreciate how important Mo has been to our team," Ferry said in an e-mail to The Associated Press. "We have had a great start. We have been really good on both ends of the court, have the top record in the league, and thus far have led the league in point differential by a wide margin all year long.
"Our players and coaches know how important Mo has been to our team's success. Regardless, we have done a great job of not getting distracted and staying focused on our team goals. I am confident we will continue to do so."
Nelson also must be replaced in the skills challenge on All-Star Saturday night.