The decision by Mattingly comes on the heels of Guerra's third blown save of the season on Sunday against the Chicago Cubs.
Mattingly informed Guerra of the decision several hours before the game. He later hinted to reporters that Guerra won't necessarily take over the eighth-inning setup role that Jansen is vacating because he wants to ease Guerra back into situations in which he can hopefully regain his flagging confidence.
"I have said all along I didn't want to have to do this," Mattingly said. "But really, it's one of those things where I don't want to be hard-headed, either. ... The game will tell you when to do it. With Javy, the game made the decision. I didn't have to make it. The game made it for me."
Although Mattingly didn't identify a primary setup man, the most likely candidate for the eighth-inning role probably is right-hander Josh Lindblom, who arguably has been the Dodgers' best reliever this season, posting a 2.35 ERA in 13 appearances -- his ERA would be even more impressive if not for a lone bad outing in which the Colorado Rockies tagged him for three runs in two-thirds of an inning.
Jansen has a 2.70 ERA and is averaging 14.6 strikeouts per nine innings after setting a major league record with 16.2 per nine innings last year, but he also has been inconsistent -- he has two saves and one blown save, and his career ninth-inning ERA is 5.59 compared to 0.70 in the eighth -- and he is getting the job on a trial basis.
He is going to get the first shot at it,'' Mattingly said. "Kenley, with all the strikeouts, really profiles more as that guy, but the ninth inning is a different animal.''
Mattingly also declined to assign a specific role to Guerra, who took over the closer's role midway through last season and saved 21 games as a rookie.
"I will use Javy all over," Mattingly said. "We're going to try to get (his confidence) back as much as anything else because he is going to be a valuable guy. We are going to need big outs from all our guys no matter how you define their roles."