The club also announced that it has unconditionally released outfielder Vernon Wells, who was designated for assignment a week ago to create room on the 40-man roster for left-handed reliever Matt Thornton.
The Yankees have no remaining unsigned players eligible for salary arbitration. They have not had a case go to arbitration since 2008, when they defeated pitcher Chien-Ming Wang.
Friday's deals, while expected, have inched the Yanks closer to exceeding their stated goal of a payroll that resides at or below $189 million. The Associated Press reported that the Yankees' luxury tax payroll sits at about $181.5 million for 19 players with agreements.
Managing general partner Hal Steinbrenner said this week that the team still has some winter shopping yet to be completed, stating, "Starting pitching is an area [in which] I believe we still need some help. We're looking at a number of possibilities and we're talking to a number of people."
If, for example, the Yankees are able to sign Japanese right-hander Masahiro Tanaka, that deal would essentially ensure that club will exceed $189 million in 2014. The rest of the free-agent starting market is headlined by Matt Garza, Ubaldo Jimenez, Ervin Santana and Bronson Arroyo.
Gardner, 30, set single-season career highs in hits (147), doubles (33) and home runs (eight) in 2013. A .273 hitter who logged 10 triples and 24 stolen bases, Gardner became the first Yankees player since Snuffy Stirnweiss in 1945 to collect at least 30 doubles, 10 triples and 20 steals in a single season.
Gardner projects to play either left field or center field this year. It has been widely speculated that Jacoby Ellsbury will take over duties in center field, but manager Joe Girardi has said that he would prefer to wait until Spring Training before locking that in.
Kelley, 27, was 4-2 with a 4.39 ERA in a career-high 57 relief appearances last season. His 71 strikeouts in 53 1/3 innings were the eighth-best mark among American League relievers, and he is expected to fill a setup role this season.
Nova, 27, is currently projected as the No. 3 starter after going 9-6 with a 3.10 ERA in 23 games (20 starts) over two stints with New York last year. He finished strong after an early-season demotion to the Minors, going 7-5 with a 2.70 ERA in 17 games (16 starts) after returning in late July and was named as the AL's Pitcher of the Month for August.
Robertson, 28, enters the season in line to succeed Mariano Rivera as the Yanks' closer. Robertson was 5-1 with a 2.04 ERA and three saves in 70 appearances in 2013, and he is the only pitcher in history to record at least 10 strikeouts per nine innings pitched in each of his first six Major League seasons (2008-13).