The Colorado Rockies acquired infielder Marco Scutaro from the Red Sox for right-hander Clayton Mortensen on Saturday in a surprising trade that could pave the way for top Boston prospect Jose Iglesias to take over at shortstop sooner than expected.

The 36-year-old Scutaro hit a career-high .299 for the Red Sox last season, when he had seven homers, 26 doubles, 54 RBIs and a .358 on-base percentage. Boston picked up his $6 million option in October, a month after the team missed the playoffs following a record collapse down the stretch.

Scutaro was expected to remain Boston's starting shortstop this season but he will play second base and bat second in Colorado, where the Rockies also have added Michael Cuddyer and Ramon Martinez in an offseason makeover following last year's disappointing slide.

Mortensen, 26, went 2-4 with a 3.86 ERA in 16 games between the Rockies' rotation and their bullpen last season. He provides depth for a Boston rotation that will be without injured starters John Lackey and Daisuke Matsuzaka next season.

The Rockies targeted Scutaro for months and taking on his $6 million contract gives the Red Sox financial flexibility to make a run at free-agent pitcher Roy Oswalt.

Shortstop has been a trouble spot in Boston since Nomar Garciaparra was traded during the World Series championship season of 2004. Orlando Cabrera filled the position the rest of that year, but he was followed by Edgar Renteria, Alex Gonzalez, Julio Lugo and Gonzalez again; Jed Lowrie, Nick Green and Alex Cora were also in the mix.

Scutaro provided two years of stability after signing with Boston as a free agent following the 2009 season. Now he's gone, too.

The 22-year-old Iglesias appeared in 10 games for the Red Sox last year, getting two hits in six at-bats. A slick fielder who has struggled at the plate as a pro, he batted .235 with a homer and 31 RBIs in 101 games for Triple-A Pawtucket last year. In two minor league seasons since he defected from Cuba, Iglesias has a paltry .308 on-base percentage and .316 slugging percentage.

Still, his defense is considered outstanding and the Red Sox have been grooming him as their shortstop of the future.

Other options for Boston include versatile veterans Mike Aviles and Nick Punto. Both have plenty of big league experience at shortstop, but they were expected to fill utility roles off the bench this season.