Nationals General Manager Mike Rizzo, left, and then-Special Adviser Davey Johnson talk behind the batting cage during batting practice prior to a game on April 3 in Washington against Atlanta. (Diamond Images)

Some will speculate that Washington Nationals General Manager Mike Rizzo had a long-standing plan to hire Davey Johnson as the ballclub’s manager.

They’ll choose to believe Rizzo and Johnson must have had a secret agreement in place ever since Johnson joined Rizzo’s staff as a senior adviser. Rizzo was simply waiting for the right time, the thinking will go, to replace Jim Riggleman with Johnson.

Such thoughts would be incorrect. Johnson’s return to managing after a decade-plus break was not part of Rizzo’s grand design for the franchise’s future. What is true, though, is Rizzo really needs this to work.

 Regardless of the unexpected sequence of events that resulted in his return to the dugout, Johnson now must succeed at a high level, not only for the remainder of this season but especially in coming seasons. All in on Rizzo’s strategy, the Lerners are writing big checks based on his recommendations and, rightfully, expect to soon receive significant returns on their baseball investments.

The Nationals’ current surprising stretch is a nice start, and Johnson is experienced at guiding teams with a variety of rosters, so he’ll at least begin in a good place despite the momentary front-office upheaval caused by Riggleman’s abrupt resignation late last week. Where Johnson goes from here, in large part, will help determine how long Rizzo continues in his job.

In Major League Baseball, every general manager occasionally errs in signing free agents. They sometimes make mistakes in assessing a club’s strengths and weaknesses. Draft picks often fail to progress in the minors.

To a degree, owners accept those errors as the cost of doing business. Blowing it in selecting two managers generally is not a forgivable offense.

Picking a manager is among a general manager’s most important duties. Many longtime baseball people will tell you there’s no bigger decision for the person who runs a club’s entire baseball operation.

If a GM can’t get it right in hiring a field boss, they say, there’s not much else he should be trusted to do. In turning to Johnson, Rizzo is backing his second Nationals manager in two years.

The last one was so frustrated with Rizzo he decided to quit before the all-star break despite possibly ending his baseball career. Because of that, Rizzo probably needs a home run with manager No. 2.

Although managers have limited influence over the outcome of games, the good ones do some of their best work before the first pitch. The top guys are skilled tacticians and successful psychologists. They listen well and see everything.

Great managers understand the makeup of everyone on the 25-man roster. It’s about knowing the right buttons to push and, most importantly, when to push them.

That’s what I learned from Johnson. The lessons occurred daily over two seasons when he led the Los Angeles Dodgers.

Johnson, who began managing the Dodgers in 1999, won a World Series with the New York Mets. He also guided Baltimore and Cincinnati to division championships during a 14-year career most managers would envy.

Rupert Murdoch’s News Corp. was in its second year in control of the Dodgers. Johnson was the high-profile manager brought in to lead a team with one of the sport’s highest payrolls and championship expectations.

His tenure in Los Angeles ended quickly. The Dodgers fired baseball’s winningest-active manager at the time because he didn’t win enough.

Johnson wasn’t the problem. He was still sharp. He continued to utilize mathematical trends well. He made the correct right-handed-vs.-left-handed decisions. If a situation called for a double-switch, he made the move. Johnson also had good hunches.

What he didn’t have was a strong working relationship with Kevin Malone, the club’s general manager at the time. On different pages from the start, Johnson and Malone simply couldn’t coexist, and ownership fired Johnson first.

Johnson won’t have that problem in Washington. Rizzo has great respect for Johnson, whose counsel he has relied on since Johnson joined the Nationals prior to the 2010 season. He just gets it about how to handle both high-ceiling youngsters and established veterans.

Knowing Johnson, he didn’t agree to come out of semi-retirement cheaply. The Lerners got Riggleman at bargain-basement prices because he had no other options. Riggleman was eager to manage again in the majors and took the low deal they offered.

When you’ve won a World Series and five division titles as Johnson has, that commands respect and Rizzo isn’t stupid. Riggleman’s decision to quit reflects most poorly on Riggleman — but it didn’t help Rizzo’s image within the game, either.

Rizzo needed to make a big hire and he did. Someone with Johnson’s credentials brings credibility to a crisis situation. For the Nationals, no matter how much the Lerners committed to get Johnson, they can’t put a price on what he brings them in the short term.

 The long-term results will depend on whether Johnson, 68, still has his old touch after last managing in the majors on Oct. 1, 2000. Johnson was ejected that day in the second inning of the Dodgers’ 4-0 season-ending road loss to San Diego.

After the game, I shook Johnson’s hand and wished him well, correctly figuring his time with the Dodgers had ended. “I’m going fishing,” Johnson said, followed by his hearty laugh. “Not sure if I’ll ever be back.”

Well, Johnson is back now, and the Nationals need him to be as good as he ever was. Rizzo especially.