Kimbrel made the roster to start the 2011 season as the team's primary closer. He was successful in his first four save opportunities before blowing his first career save on April 21, 2011. On June 3, 2011 in a game versus the New York Mets, Kimbrel passed the record for most saves by a National League rookie before the All-Star break. He is the fastest Braves pitcher to reach 100 career strikeouts, doing so in 59 ⁄3 career innings. His new record surpassed the previous record set by John Rocker in the 1998–1999 season, where it took Rocker 70 career innings to reach the 100 career strikeout mark. On July 5, his 26th save matched Jonathan Papelbon's record for most saves by a rookie before the All-Star break. On July 7, Kimbrel's 27th save of the year against the Colorado Rockies broke Papelbon's record.
On July 22, 2011 in a game versus the Cincinnati Reds, Kimbrel broke the Braves rookie record for saves in a season (31).
On August 9, 2011 in a game versus the Florida Marlins, Kimbrel tied the National League rookie record for saves in a season (36 by Todd Worrell of the St. Louis Cardinals in 1986). He broke that record on August 17 in a game versus the San Francisco Giants. On August 21, 2011, Kimbrel recorded his 100th strike out which coincided with his 39th save of the season and a string of 30 ⁄3 innings without yielding a run. On August 23, 2011, Kimbrel recorded his 40th save, tying the rookie save record of Neftalí Feliz. He subsequently broke this record with his 41st save on August 31 with two strikeouts in a game against the Washington Nationals. At the time, he led the majors in saves and had not given up a run in his last 34 innings. The following night, Kimbrel surpassed Cliff Lee's mark of 34 scoreless innings with 34 ⁄3 scoreless innings for the longest scoreless streak in the majors in 2011. He was named the NL Rookie of the Month and MLB Delivery Man of the Month for August 2011. His scoreless inning streak came to an end after 38 ⁄3 innings, on September 9, 2011.
Kimbrel's four-seam fastball was the 12th-fastest among Major League relievers in the 2011 season. In addition, he threw the hardest curveball, averaging 87 mph. His fastball had the fifth-highest whiff rate among relief pitchers (32%), and he also had the highest whiff rate of any reliever's curveball, at better than 55%. His pre-pitch stance has also been widely noted and has been dubbed "Kimbreling", or "How to Destroy Your Back by 35", or "Spider Arms".