Casey Janssen’s fastball has never averaged 92 mph, and last season it was around 89 mph. (Jonathan Newton/The Washington Post)

Over the past five years, Casey Janssen has been among the steadiest relievers in baseball. The former closer had a 2.99 ERA and 83 saves pitching in the bandboxes of the American League East. He accomplished this without an overpowering arsenal of pitches. His fastball has never averaged more than 92 mph for an entire season, most often sitting at 90-91. Yet in an era in which pitchers are throwing harder than ever, Janssen has found his niche.

“They said I topped at 95 once,” Janssen said. “I joke that it was probably downhill and downwind.” Actually it was 97 mph once — in 2007, his second year in the majors. That year, his fastball averaged 91.7 mph.

“He’s certainly not overpowering, but he has fastball command,” Toronto Blue Jays pitching coach Pete Walker said. “He can locate his fastball with the best of them.”

The Washington Nationals hope Janssen’s savvy and guile will help solidify the back of their bullpen as the likely successor to longtime setup man Tyler Clippard. Janssen, 33, is coming off his worst season since 2009. A bad second half (6.46 ERA) and food poisoning he contracted during the all-star break undermined his dominant first half (1.23 ERA). The right-hander signed a one-year, $3.5 million deal with a mutual option for 2016 with the Nationals.

Janssen may be at the age of decline — his fastball averaged a little more than 89 mph last season and his strikeout rate fell to 5.5 per nine innings — but his command and smarts have helped him evolve.

Post Sports Live discusses the major story lines from Nationals spring training, including who will be the Opening Day starter and how Ryan Zimmerman will transition to playing first base. (Post Sports Live/The Washington Post)

“A lot of times when you’re the best, it’s at that point when you start to decline at your strength and conditioning,” Janssen said. “The mental side of the game takes way over. You learn it’s about being efficient. It’s about setting up hitters. You’re not as stubborn. The whole thing of ‘I wish I knew then what I know now’ is true. You learn the hard way. If you actually learn from those experiences, you can stick around in this game a long time.”

Janssen has flourished most of all because of his command. In 50 appearances last season, he walked only seven batters. During his three years as Toronto’s closer (2012-14), he posted a walk rate of 1.7 per nine innings.

“When you don’t throw hard, you pretty much have to be perfect with your command,” he said. “It’s not ‘here it is, hit it.’ There’s a reason behind it and a high level of execution that’s necessary.”

At Fountain Valley High in Orange County, Calif., Janssen threw between 86 and 88 mph. At UCLA, Janssen’s fastball ticked up to 88-91 mph. He first reached the majors in 2006 as a starter with the Blue Jays. When he was converted full time to a reliever in 2010, he could throw harder because he didn’t have to save himself for so many innings per outing.

His time as a starter taught Janssen how to pitch. He learned how to attack hitters and disrupt them with location and timing, and he fine-tuned his command. His stint as a part-time position player in college also taught him how to read swings. He looks for even the slightest of flinches from the batter to gauge what his next pitch will be.

“I have a nice ability to read that stuff and to understand what hitters are trying to do,” he said.

Janssen has several philosophies that have helped him, too. He loves the bottom of the strike zone. As a result, Janssen’s career groundball percentage is 47.1 percent, including last season’s career low of 34.4 percent. “I don’t want anything higher than the knee unless it’s intentional,” he said.

A confident Bryce Harper reported to Nationals spring training in Viera, Fla. When asked about adding Max Scherzer to the starting rotation, he said, “I just started laughing. I was like, where’s my ring?” (The Washington Post)

Janssen also swears by the first-pitch strike. “Best advice I got was from B.J. Ryan: ‘You’re a boxer, and you want to be the guy throwing the haymakers,’ ” Janssen said. And part of that is pace. Janssen has averaged about 23 seconds between pitches in his career.

“What I loved about him when I was a shortstop and he was pitching, he worked quickly,” said Yunel Escobar, who was teammates with Janssen in Toronto from 2010 to 2012. “He doesn’t let the batter think. Sometimes when you take your time getting into the batter’s box, you almost have to ask for time from the umpire because he doesn’t let you get settled.”

Janssen has many ways of attacking hitters: He throws a fastball, curveball, cutter, change-up and slider; the first three are his best pitches. “He confuses you at the same time with movement and with his pitches,” Escobar said. His cutters in and curveballs on the outer edge of the plate have helped him neutralize left-handed batters (.689 career OPS) as well as right-handed batters (.692).

The bullpen will take a slightly different form in 2015 with Janssen in the fold. He may not carry Clippard’s workload — Clippard averaged 79 innings the past five years; Janssen averaged 57 innings in that span. But Janssen believes he is ready to pitch more this season and prove he is still effective. As he has most of his career, Janssen has found a way.

“The game is always evolving, and you want to be a step ahead on the mound as well,” he said. “As long as you can do that, velocity is secondary to the mental side.”

Notes: Tyler Moore continued his torrid start as the Nationals took their second come-from-behind victory, 9-8 over the Atlanta Braves. Moore had two doubles in Thursday’s night’s win over the Mets and had a homer and triple Friday. He also misplayed a ball in right field. . . .

Nationals starter Jordan Zimmermann threw two scoreless innings after leading off the game with a walk, an uneventful first start of the spring.

Taylor Jordan and Craig Stammen struggled in relief. Jordan’s fastball was more out of control than normal, and Stammen was shaking off the early season rust. Jordan gave up three runs on four hits in one inning, though Matt Williams said he changed speeds well. Stammen gave up five runs on eight hits in ­1 2/ innings.

“We know the more he throws, the better he gets,” Williams said. “We pushed him a little bit today, just to get him into the flow. I have no worries about Stammer.” . . .

Escobar planned to see a doctor Friday after experiencing soreness in his back.