The Red Sox have signed free agent third-baseman Adrian Beltre to a one-year deal with an option for 2011, and the top-notch defender should pair with new shortstop Marco Scutaro to provide Boston with stellar infield defense this season.

Pending a physical, Beltre will sign a one-year deal with a base salary of $9 million this season. He would have a $5 million player option for 2011 and a $1 million buyout, guaranteeing him at least $10 million.

The terms of the deal were first reported by NESN's Peter Gammons.

Beltre, a premier defensive third baseman, has settled into a groove as an above-average offensive performer after one amazing, aberrant season in 2004.

Beltre, 30, made his debut in 1998 at the age of 19, for the Los Angeles Dodgers. From 1999 to 2003, he emerged as an excellent defensive third baseman good for a roughly .275 average, 20 home runs, double-digit stolen bases and a decent on-base percentage. Then, in his contract year of 2004, Beltre absolutely exploded, setting career highs with a .334 average (.388 OBP), 48 home runs, 121 RBI and 104 runs scored.

After signing a five-year, $64 million deal with Seattle that winter, he immediately returned to earth, again posting his standard .275 and 20-plus home run totals.

Beltre spent a month on the disabled list this season with a severe contusion to his right testicle. Partly due to the injury, he posted a .265 average with eight home runs, 44 RBI, and a .304 on-base percentage.

Beltre's acquisition means the almost-certain departure of veteran third baseman Mike Lowell. The Sox had tried to trade Lowell to Texas during the Winter Meetings earlier this month, but the trade fell apart over concerns about Lowell's injured thumb. The thumb later required surgery, though Lowell should be full strength by spring training.

He might begin spring training with the Red Sox, but chances are, once he shows he's healthy, he'll open the year with another team. The Red Sox will likely have to pick up most of Lowell's $12 million 2010 salary to deal him.

Beltre is one of four major new acquisitions for the Sox this winter. Although the team let left fielder Jason Bay depart in free agency, it brought in standout starting pitcher John Lackey, shortstop Scutaro, and outfielder Mike Cameron. Boston also acquired backup outfielder Jeremy Hermida, while letting 2009 Sox Alex Gonzalez and Rocco Baldelli depart in addition to Bay and likely Lowell.

Now, Boston has numerous options across the infield. Former Gold Glover Kevin Youkilis should settle in as the starting first baseman, with Dustin Pedroia at second, Scutaro at short, and Beltre at third. Youkilis can also play third, while catcher Victor Martinez and backup Casey Kotchman should get time at first base. Jed Lowrie is the leading candidate for the utlity infielder's job.