BOSTON — When the diagnosis came during spring training of 2015, it was terrible news for catcher Christian Vazquez. He needed Tommy John surgery and would miss the season.

But from the ashes of that disastrous time rose the stellar catching tandem the Red Sox enjoy today.

Without Vazquez’s injury, Boston does not have Sandy Leon.

Now the Red Sox have both players – arguably the best defensive duo in the game – healthy and performing with a hot bat to begin 2017.

Back in March 2015, Leon was not in the plans. The Red Sox idea was to have Vazquez and the newly acquired Ryan Hanigan behind the plate. Blake Swihart was coming off an impressive 2014 in Portland but wasn’t ready for the majors.

When Vazquez’s elbow betrayed him in late March, the Red Sox looked for available catchers. The Nationals offered Leon, who seemingly had little future – .189 average in 34 major league games over three seasons – and was out of minor league options.

Washington sent Leon to Boston for “cash considerations,” a term meaning “not much.”

Leon didn’t impress initially. When Hanigan was hurt in May, Boston called up Swihart, giving him most of the playing time.

Leon batted .184 in 41 games and was designated for assignment on July 20. Nobody claimed him. Leon, on a minor league deal, went to Pawtucket.

In 2016, Leon was back on the 40-man roster and assigned to Pawtucket. He was called up on June 5 when Hanigan was hurt.

But this was a new Leon, a switch hitter who worked hard on an improved batting stance – more upright, better balanced. He seemed in control at the plate instead of overmatched.

Leon hit .417 in June.

Fluke, right? Leon remained above .300 through July, then August.

“Start getting over 125 at-bats, you can’t say he’s hitting into good luck all the time,” Manager John Farrell said. “He was driving the ball from both sides of the plate.”

Leon finished the year with a .310 average, the highest for a Boston catcher since Carlton Fisk (.315) in 1977.

Vazquez never got traction in 2016, catching 57 major league games and batting .227.

Heading into this year, Boston knew it had two good defensive catchers, but there were questions. Could Vazquez hit? Was Leon a one-year wonder?

So far, so good. Vazquez, despite going 0 for 4 on Friday night, is batting .296. Entering Saturday’s game, he was 5 for 8 in three games, with two doubles and a triple. He was batting .625.

“In the early going it’s been a welcome addition,” Farrell said. “Still, their impact has been felt most behind the plate.”

Not only do pitchers rave about both catchers’ pitch-calling and receiving abilities, the two have thrown out 6 of 7 base-stealers.

That’s no fluke. Over the last 30 years, Vazquez leads all catchers (minimum 100 starts as a catcher) with a caught-stealing percentage of 46.4. Leon is No. 2 at 44.3 percent. Ivan Rodriguez is next at 41.7.

“On both sides of the ball, they’ve done an excellent job,” Farrell said.

Neither Leon, 28, nor Vazquez, 26, is eligible for free agency until 2021. That brings up the issue of Swihart, 25, who is in Pawtucket. He’s an obvious talent but is guilty of not being as good defensively as two of the game’s best defensive catchers.

The Red Sox tried Swihart in left field last year and he ended up with a severely sprained ankle that required surgery. That experiment seems done, especially with Andrew Benintendi cemented in left.

Swihart is out of minor league options after this year.

For now, it’s a good problem to have.

REMEMBER THE 2008 draft, when Boston went after catchers early and often? Vazquez was the third catcher the Red Sox chose, in the ninth round out of high school in Puerto Rico.

Before Vazquez the Red Sox opted for college catchers, Ryan Lavarnway in the sixth round and Tim Federowicz in the seventh. They played together in Portland in 2011.

Federowicz, 29, was traded to the Dodgers later that year. Since then he’s been with the Padres’ organization, and the Cubs last year, including 17 major league games.

Federowicz signed with the Giants this year and recently was called up to fill in for the injured Buster Posey.

Lavarnway played parts of four years with Boston and was waived after the 2014 season. Since then he’s played in the Orioles, Braves and Blue Jays organizations. Signing with Oakland this year, he’s in Triple-A.

THE SILLY quote of the week comes from Orioles Manager Buck Showalter, regarding the Red Sox flu outbreak. Showalter, who enjoys needling the Red Sox, especially their big-market clout, said his players also battled the flu big.

“Our guys have fought their way through it,” Showalter said. “I know we’ve got a lot of guys that aren’t 100 percent with it, but so do a lot of clubs.

“Nobody wants to hear somebody else complain about it. Our guys have done a good job not broadcasting it to the world.”

There is a difference between “broadcasting it to the world” and explaining why a regular player isn’t in the lineup or even at the stadium.

Kevin Thomas can be reached at 791-6411 or:

[email protected]

Twitter: @ClearTheBases