Guerra, who saved 21 of 23 opportunities in his rookie season after Jonathan Broxton was injured, remains the closer this year -- even though Jansen has the electric stuff that set a Major League record for strikeout frequency (11.6 per nine innings) last year.
Taking nothing away from Guerra, who has battled back from Tommy John surgery, but scouts project Jansen as the most likely eventual closer because of his stuff and intimidating size.
Has manager Don Mattingly considered swapping their roles?
"It's hard not to with those two, with what Kenley is able to do," Mattingly said. "You guys look at what happened at the end of the season [when Jansen was unhittable], but you don't think about what happened in the beginning [when Jansen was sent to the Minor Leagues]. It's hard not to think of Kenley like [a closer]. But go back to Javy, he took the role and didn't drop the ball. It's hard to say he didn't do the job. He did the job."
And it's his job to lose. Mattingly said when he talked to the two about the potential for friction, he found that Guerra and Jansen had already talked to each other and are on the same page as him.
"I told them, 'I don't know what the right decision is,'" Mattingly said. "If they both throw the way they can, it's a tough call. I know Kenley would like to close. What both said is that when we get to the eighth inning, the game's over -- and that's what you want to hear. It's not Kenley wanting to close and looking for Javy to stumble when we're trying to win a game. The game is going to tell me what to do -- it will tell me to keep it like this, to swap them, to use [Mike MacDougal]. The game will tell me."
No matter the choice, with Broxton and Hong-Chih Kuo gone, Mattingly has turned over game-ending situations to youth. The 24-year-old Jansen has one year and 73 days of Major League experience -- four more days of service than the 26-year-old Elbert. Guerra, also 26, has 137 days of service.
Jansen was the most efficient on Wednesday, with one strikeout and two popups. Elbert allowed a hit and a walk, although the latter could have been a strikeout. Guerra was wild -- with a pair of walks -- but the A's assisted with an inning-ending strikeout-caught stealing double play.
"I'm pleased with the way I feel," said Jansen. "I'm just focusing and feeling that zone again, staying consistent and getting ahead of every hitter."
"I felt really good for the first time back out there," said Elbert, who resurrected his career after dealing with stress in 2010. "I didn't have command of the slider the way I like, but put my heater in the right spots and threw strikes."
"It was good to get back on the mound at game speed," said Guerra. "I just had to tone the emotion down. I got a little jumpy, a little too quick to the plate and made a simple adjustment."
Does Mattingly have any qualms about the inexperienced trio, even after last year's success?
"A little," Mattingly conceded. "But I'm not afraid of young guys. Older guys were young at some point. It doesn't mean they're not able to keep up. You see their temperament, their work ethic, the attention they pay to get better. Usually when you see that, you're okay.
"This is part of the dynamics from one year to the next. I don't really worry about it. The first time they get paid [meaning multi-year], you worry about. After that, you make sure guys don't become complacent. They've reached a lot of personal goals, other than the winning part. Established guys need to have that burn to get better."
The veterans with guaranteed salaries who are slated to pitch on Thursday -- Matt Guerrier, MacDougal and Todd Coffey -- will fill the middle innings, with a long reliever to come from Josh Lindblom or the group of non-roster invitees headed by vets Jamey Wright and John Grabow.
"You want a mixture," said Mattingly. "We've got older guys that have done those jobs. Todd set up. Mac set up and closed. Matt has set up. They've been through things the younger guys will be going through. And if you need to talk, you hope those guys speak up."
Ken Gurnick is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.