In his first season as a relief pitcher, Davis went a combined 8-3 with five saves and a 2.71 ERA in 48 appearances with Double-A Harrisburg and Triple-A Syracuse.
Davis, 26, is 3-0 with a 0.56 ERA and .155 batting average against in 14 appearances this offseason with Gigantes del Cibao of the Dominican Winter League.
Acquired from the Padres in a trade for infielder Alberto Gonzalez in the spring of 2011, Davis is 45-24 with five saves and a 3.84 ERA in 146 games during five Minor League seasons.
Karns, ranked by MLB.com as the Nationals' No. 16 prospect, was named the organization's Minor League Pitcher of the Year after going a combined 11-4 with two saves and a 2.17 ERA in 24 games this past season with Class A Hagerstown and Class A Potomac. The 24-year-old led all Washington pitchers in ERA and strikeouts (148), while his win total ranked tied for second.
Selected in the 12th round of the 2009 First-Year Player Draft, Karns is 14-6 with two saves, a 2.21 ERA and 10.9 strikeouts per nine innings in 37 games during two professional seasons.
Players who were signed when they were 19 or older and have played in professional baseball for four years are eligible for the Rule 5 Draft, as are players who were signed at 18 and have played for five years. Clubs pay $50,000 to select a player in the Rule 5 Draft, held at the conclusion of the Winter Meetings on Dec. 6 in Nashville, Tenn. If that player doesn't remain on the 25-man roster for the full season, he must be offered back to his former team for $25,000.
Bill Ladson is a reporter for MLB.com and writes an MLBlog, All Nats All the time. He also could be found on Twitter @WashingNats. This story was not subject to the approval of Major League Baseball or its clubs.