LaMarcus Aldridge says he has decided to go with the Spurs

Highly coveted free agent LaMarcus Aldridge will sign with the San Antonio Spurs, he said Saturday on Twitter.

His deal will be a four-year maximum contract worth more than $80 million, with an opt-out after the third year, a source told ESPN's Marc Stein.

Sources said the pitch Aldridge received Friday in Los Angeles ‎from Spurs coach Gregg Popovich -- about playing with Tim Duncan his final days in the NBA and then taking over for him as the Spurs' frontcourt linchpin alongside Kawhi Leonard -- resonated strongly with Aldridge.

It was the Spurs' second meeting with Aldridge. Popovich, Duncan, Leonard and Tony Parker all pitched Aldridge directly Wednesday morning, sources said.

Parker welcomed Aldridge aboard Saturday:

Spurs forward Kyle Anderson, playing in summer league for the team, said of Aldridge's announcement: "That's great news, great news. He's a dominant post presence. He can score off either shoulder; can score out to 19 feet. He's a great passer, very unselfish. So that fits in perfect with the system here."

When asked if there was a better starting lineup in the league than Aldridge, Duncan, Leonard, Parker and Danny Green, Anderson said, "That's a tough starting lineup right there. I'm not one to say who is the best, but that's pretty tough right there."

San Antonio's odds to win the West improved to 2-1 with the news, besting Oklahoma City and defending champion Golden State. The Spurs are 4-1 to win it all, behind only Cleveland (9-4).

Aldridge, who had spent his entire nine-year career with the Portland Trail Blazers, also met twice with the Los Angeles Lakers and entertained offers from the Houston Rockets, Dallas Mavericks, Phoenix Suns, Toronto Raptors and Miami Heat.

Sources told Stein that the signing of Aldridge all but clinches that Popovich, at the very least, will coach beyond Duncan's playing career as opposed to walking away when the future Hall of Famer finally retires, as Popovich has joked about on many occasions.

ESPN.com reported in May that the extension Popovich landed from Spurs owner Peter Holt after the team won the 2013-14 championship was for five years and $55 million, which surprised some observers because of its length. But Holt, in an interview with ESPN Radio during All-Star Weekend, said he thinks Popovich will actually see out the entire contract on the bench.

"He and I are roughly the same age," Holt said. "In five years, he'd be 70. If his health holds up, I know he doesn't believe it, but I believe he'll stay. He'll be there."

Aldridge, 29, was drafted second overall by the Chicago Bulls in 2006, but was traded on draft night to the Trail Blazers for Tyrus Thomas and Viktor Khryapa. He made four All-Star teams during his nine-year career with the Blazers, and was named second-team All-NBA this season after two third-team selections (2011, '14).

Aldridge had been the central building block for the rebirth of the Blazers, becoming the franchise's second all-time leading scorer last December, second only to the legendary Clyde Drexler. Aldridge became the franchise's all-time leading rebounder in March, passing Drexler. He's averaged more than 20 points per game each of the past five seasons, finishing with a career-high 23.4 this past season with 10.2 rebounds per game in 71 appearances (all starts).

Following the 2009-10 season, Aldridge signed a five-year, $65 million extension with the Blazers. He was part of trade rumors for much of the 2013 offseason, but expressed a desire to remain with the organization while also speaking candidly about wanting the roster improved around him. The Blazers finished fifth in the Western Conference with 54 wins, with Aldridge leading them to a first-round victory over the Rockets. They won 51 games last season, finishing fourth, but were knocked out in five games by the Memphis Grizzlies.

Aldridge had a career year last season despite playing most of it with a torn ligament in his left thumb suffered in late January. After initially being ruled out six to eight weeks with expected surgery, Aldridge opted to play through the injury, missing only two games.

In 648 games, Aldridge holds career averages of 19.4 points and 8.4 rebounds in 35.5 minutes per game.

The 6-foot-11 power forward grew up in the Dallas-Fort Worth area and spent two years at the University of Texas in Austin -- about 80 miles from San Antonio -- before declaring for the 2006 draft.

ESPN.com's Michael C. Wright and Royce Young contributed to this report.