Kenley Geronimo Jansen (born September 30, 1987) is a Curaçaoan professional baseball pitcher who is a free agent.

He has played in Major League Baseball (MLB) for the Los Angeles Dodgers, Atlanta Braves and Boston Red Sox.

After 11 years in the major leagues with the Dodgers, he entered free agency and signed a one-year deal with the Braves in 2022.

[1] After the season, he again played in Hawaii Winter Baseball, this time for the West Oahu CaneFires[7] In 2008 with the Loons, he hit .227 and 9 home runs in 79 games.

In the Netherlands' upset of the favored Dominican Republic team, Jansen threw out Willy Taveras on an attempted steal of third base in the ninth inning, a key play in the game.

Under the tutelage of former major leaguer Charlie Hough, he made the conversion in the second half of the 2009 season at Inland Empire.

[13] He made his Major League debut in relief on July 24 against the New York Mets, where he pitched a scoreless inning, retiring all three batters he faced and striking out two.

[15] On August 26, Jansen walked and scored a run in his first Major League plate appearance, in Milwaukee against Yovani Gallardo of the Brewers.

[20] At the end of the season, after missing some time due to heart problems, Jansen was replaced as closer by Brandon League.

[5] He became just the fourth Dodger pitcher in history with at least 40 saves in a season, joining Éric Gagné (who did it three times), Todd Worrell, and Jeff Shaw.

[31] Jansen eventually struck out 27 before he finally walked a batter on June 30, eight shy of the major league record.

[35] On June 20, Jansen picked up his 162nd career save against the Washington Nationals, breaking the Dodgers franchise record, previously held by Gagné.

[45] The previous record was held by Cardinals starting pitcher Adam Wainwright, who struck out 35 batters before giving up a walk in the 2013 season.

[46] The streak eventually reached 51 strikeouts before he issued his first walk of the season, giving Nolan Arenado of the Colorado Rockies a base on balls on June 25.

[5] Jansen allowed two runs to score, including a solo homer by Marwin González in Game Two of the 2017 World Series against the Houston Astros.

In his second inning of work, he hit Brian McCann with two outs and then after a walk, he gave up a walk-off single to Alex Bregman.

[5] Jansen was bothered by an injury during spring training and was slow-played after his 2017 workload, resulting in two blown saves during a shaky April.

[58] But on May 5, pitching for the third day in a row, Jansen walked a batter and allowed two bunt singles to load the bases with no outs.

[60] On September 25, in a game against the San Diego Padres, Jansen picked up his 300th career save, becoming the 30th pitcher all time and the first in Dodgers history.

[66] On August 25, Jansen became the twelfth reliever in MLB history to record 1,000 strikeouts by striking out Austin Nola of the San Diego Padres.

[70][71] He made his Braves debut on April 8, surrendering 3 earned runs in the 9th inning against the Cincinnati Reds in a non-save situation.

On April 20, he earned the 425th save of his career, passing John Franco for sole possession of fifth place on the major-league all-time list.

In the Netherlands' upset of the favored Dominican Republic team, Jansen threw out Willy Taveras on an attempted steal of third base in the ninth inning, a key play in the game.

[80] After initially saying he would not pitch in the 2017 tournament, having signed a five-year $80 million contract with the Dodgers in the offseason, Jansen again joined the team when they advanced to the semi-finals.

[86] Jansen was diagnosed in 2011 with an irregular heartbeat (specifically, atrial fibrillation), and he missed some time that season while he was placed on blood thinners to prevent clots.

However, the heart medication he took, which included beta blockers, had the side effects of leaving him feeling fatigued and unemotional.

[93][94] He gave up four home runs in his first two outings back, blowing both save opportunities, and after he protested the effects of his medication his doctors switched him to aspirin.

[57] Jansen completed the season and provided scoreless relief in seven of nine postseason appearances, allowing two runs in 10.2 innings (1.69 ERA).

On November 26, 2018, Jansen underwent a 5+1⁄2-hour heart ablation procedure, again performed by Koonlawee Nademanee, in Los Angeles.

Jansen dedicated himself to a healthier diet after recovering from the operation and reported to spring training 25 pounds lighter.