MIAMI -- After guiding the Miami Heat to a championship in 2006, team president Pat Riley kept the roster largely intact and bypassed the opportunity to make major changes.

Riley has taken a much different approach this time around. The Heat officially made two key veteran additions to their championship core Wednesday by signing Ray Allen and Rashard Lewis to contracts on the first day NBA teams were allowed to consummate deals with free agents.

By bringing aboard Allen, the Heat not only pick up a player who is the league's all-time leader in 3-point field goals, they also swipe a key contributor from a Boston Celtics team that was Miami's chief rival in the East.

The Heat eliminated Allen's Celtics in Game 7 of the conference finals on the way to the title.

"You move into a situation coming into the summer and you don't know potentially what could happen," Allen said Wednesday, sitting beside Riley and Heat coach Erik Spoelstra. "And here I sit."

Allen, 36, turned down a two-year, $12 million offer to return to the Celtics and accepted a three-year deal with the Heat, who were limited to only their mini-midlevel amount of just more than $3 million per season.

Lewis, 32, signed a deal for $2.6 million over two years at the veterans minimum. He also received more than $13 million in a buyout from the New Orleans Hornets after he was traded last month by the Washington Wizards.

In Allen and Lewis, the Heat gain two players who have made a career out of spreading the floor and knocking down 3-pointers. That skill set is a priority in Miami, where shooters are at a premium around LeBron James, Dwyane Wade and Chris Bosh, who led the Heat to a championship after defeating Oklahoma City in the NBA Finals last month.

"As we said a couple of years ago when we started to rebuild the team, I think it's important year in and year out that you continue to try to add quality talent and players with experience, who want to make a commitment to winning," Riley said Wednesday of his free-agency recruiting efforts. "I just mentioned LeBron and Chris and Dwyane, and they take it from there."

Ray Allen signed a three-year deal with the Heat on Wednesday, joining the team that beat the Celtics, his former team, in the East finals. AP Photo/Lynne Sladky

Allen, a 16-year veteran, has made 2,718 3-pointers and averaged 20 points over a career that has included stops in Milwaukee and Seattle before he was traded to Boston five years ago. A key member of the Celtics' Big Three alongside Kevin Garnett and Paul Pierce, Allen helped lead Boston to a championship in their first season together in 2008.

But Allen chose to walk away from the Celtics after a turbulent season, during which he was privately frustrated with trade rumors in February, issues with teammate Rajon Rondo, and an ankle injury that ultimately required surgery last month to remove bone spurs. Allen confirmed Wednesday that there were "differences" with teammates in general, but did not mention Rondo by name.

"I look back at all our time spent in Boston ... we had a lot of disappointments, but we shared a lot of thrills," Allen said. "It is sad to me that I'm not going to be with those guys anymore. But I look forward to being here."

Meanwhile, the Heat made acquiring Allen their top priority to add depth to a perimeter rotation that includes Shane Battier, Mike Miller and James Jones. Riley said Wednesday that Miller, who was hobbled by back problems late last season, is scheduled to meet with doctors again this week to determine whether surgery is necessary.

Lewis, a 14-year veteran, has been slowed by injuries each of the past two seasons and has been on a steady decline since 2009, when he helped the Orlando Magic reach the NBA Finals, where they lost to the Los Angeles Lakers.

A combination of problems with both knees and a thigh limited Lewis to a reduced role in Washington, but the 6-foot-10 forward has averaged 16.1 points and 5.6 rebounds over his career. Lewis hopes that playing with Miami's elite playmakers -- led by James, the regular-season and Finals MVP -- will help restore his productivity.

"Obviously, I'm hungry just to win," Lewis said. "I played with Orlando and got a taste of being in the Finals, getting close to winning that championship. I'm at a point in my career where I've been on an All-Star team, played 13 years ... my next goal is to try to win a championship."