To make room on the 40-man roster, the club designated for assignment infielder Micah Johnson.
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Jansen, the National League Reliever of the Year, earned his first All-Star selection in 2016, when he also rewrote the Dodgers record book.
While compiling a single-season career high of 47 saves, tying for second in the Majors, he supplanted Eric Gagne as the franchise's all-time saves leader (189). And with 632 strikeouts, he eclipsed Jim Brewer's previous Dodgers record of 604 strikeouts for a reliever.
The 29-year-old native of Curacao was second among NL relievers with a 1.83 ERA, limiting opponents to a .150 batting average, the best in MLB, as was his 0.67 WHIP and 9.45 strikeout-to-walk ratio (104 strikeouts, 11 walks). Batters were only 2-for-25 (.080) with runners in scoring position and two outs, and first batters faced hit only .092 with five walks.
In the postseason, Jansen was a horse, with seven appearances, five of multiple innings, and three saves. His eight career postseason saves are also a franchise record. He was the only Dodger to record a save in 2016, the first time since the save became an official stat in 1969.
Jansen made a career-high 51 pitches in the Dodgers' clinching Game 5 of the NL Division Series against Washington and pitched three innings in relief of Clayton Kershaw when the Dodgers were eliminated by the Cubs in Game 6 of the NL Championship Series.
Jansen's agent said Washington offered more money than the Dodgers, but Jansen preferred the comforts of returning to his only organization and the one that switched him to reliever after five obscure Minor League seasons as a catcher.
With the build of a power forward (6-5 and 270), Jansen has missed playing time because of a foot tumor and congenital heart defect, both requiring successful corrective surgery, but has never had a shoulder or elbow injury.
The contract is the largest the Dodgers have given to a relief pitcher and the largest awarded by the current front office.
With the Dodgers in search of a right-handed-hitting second baseman (namely Brian Dozier), the left-handed-hitting Johnson, 26, was the casualty of a numbers crunch, as the club needed a 40-man roster spot for Jansen.
Johnson was acquired last offseason from the White Sox with Trayce Thompson and Frankie Montas and spent the bulk of 2016 at Triple-A Oklahoma City, where he hit .261 with a .677 OPS and 26 stolen bases in 120 games before a seven-game cameo with the Dodgers in September. While at Oklahoma City, he started 78 games at second base and 34 in the outfield.