Splitter, 28, developed into an important part of the Spurs' run to the NBA Finals and had significant interest around the league as a restricted free agent.
Portland had strongly considered signing Splitter to an offer sheet near the $9 million salary that Spurs paid, but Splitter's representatives and San Antonio worked out most of the details of an agreement on Monday night and into Tuesday, sources said.
Splitter averaged 10.5 points and 6.4 rebounds for the Spurs, and will be an important part of the franchise's eventual transition beyond Tim Duncan. The Spurs drafted the Brazilian with the 28th pick in 2007.
The Spurs will turn their attention to re-signing two more of their own free agents, Manu Ginobili and Gary Neal.
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