Komatsu, who turned 24 after the 2011 season, split the year between the Brewers' and Nationals' Double-A affiliates. He was Milwaukee's Minor League Player of the Year in 2010, and was traded for Jerry Hairston Jr. at the non-waiver Trade Deadline in July 2011.
A left-handed hitter out of Cal State-Fullerton, Komatsu was an eighth-round Draft pick by the Brewers in 2008. He batted a combined .277 with a .367 on-base percentage and .382 slugging percentage in 2011, with seven homers, 48 RBIs, 60 runs scored and 21 steals in 30 attempts.
The Cardinals will pay $50,000 to Washington for Komatsu's services, and must keep him on their 25-man roster (or Major League disabled list) for all of the 2012 season. Otherwise they would be required to offer him back to the Nationals for $25,000.
In the Minor League portion of the Rule 5 Draft, the Cardinals selected two players. They took left-handed pitcher Barret Browning from the Angels' organization and right-hander Shooter Hunt from the Twins' system. They lost righty Javier Avendano and catcher Charlie Cutler in the Minor League phase.
Matthew Leach is a reporter for MLB.com. Read his blog, Obviously, You're Not a Golfer and follow him on Twitter at @MatthewHLeach. This story was not subject to the approval of Major League Baseball or its clubs.