By Matthew Geagan, CBS Boston

BOSTON (CBS) — The Boston Celtics were relatively quiet leading up the NBA’s 3 p.m. trade deadline on Thursday.

But as the seconds were counting down, Danny Ainge stepped back and turned an expiring contract and future first-round pick into another asset for the future.

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Ainge and the Celtics acquired guard Isaiah Thomas from the Suns, sending veteran guard Marcus Thornton and the Cleveland Cavaliers 2016 first-round pick to sunny Phoenix (as first reported by Yahoo! Sports’ Adrian Wojnarowski).

Thomas, whom Ainge coveted this offseason on the free agent market, averaged 15.2 points and 3.7 assists for the Suns in his first year in Phoenix, coming off the bench in all but one of his 46 games played. He should give the Celtics some instant offense off the bench for the rest of the season.

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A second-round pick in 2011 out of Washington, Thomas spent the first three years of his NBA career with the Sacramento Kings. He’s averaged 15.3 points and 4.6 assists per game in his four NBA seasons, posting a career-high 20.3 points for Sacramento in 2013-14. He is a 44 percent shooter from the floor for his career, hitting 37 percent of his shots behind the arc.

Thomas is signed for the next three seasons following 2014-15, making $6.9 million, $6.5 million and $6.2 million, respectively. He gives Boston another young guard to build around, and Ainge has the option to either keep Thomas as a part of the future or pawning him off at a later date.

The deal gives Boston a glut of young guards, with Thomas joining Marcus Smart, Avery Bradley, Evan Turner and James Young in the Celtics’ back court.

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The future is still unclear for the rebuilding Celtics, but Ainge picked up another solid building block on Thursday.