New York Yankees Masahiro Tanaka fires a pitch during the first inning of the season opener against the Toronto Blue Jays at Yankee Stadium on Monday, April 6, 2015.

NEW YORK – No matter what the Yankees say publicly, they have to be wondering whether it was the right call to delay Tommy John surgery for Masahiro Tanaka, after watching him get pounded by the Blue Jays on Opening Day. The Japanese star ominously abandoned his four-seam fastball in spring training and did so again on Monday, which means he’s either hurt or afraid of getting hurt.

Whether it’s Door No. 1 or Door No. 2, the net effect is still the same: Tanaka is a shell of the pitcher who teetered on greatness in the first half of 2014.

Instead, he lasted only four innings — working cautiously, tentatively, almost in fear of a Jays lineup that slugged the second-most HRs in the American League last year. Tanaka allowed five runs (four earned) in the 6-1 rout, prompting one talent evaluator in attendance to say the Yankees are “wasting time” by trying to work around the partial tear in Tanaka’s elbow.

The right-hander bristled at the notion that something’s wrong, but that’s just his pride taking over. More than once Tanaka said he was sabotaged merely by “falling behind” and “bad counts” but finally relented when asked why he threw so few fastballs – just 26 out of 82 pitches.

“Because they were being hit,” Tanaka admitted through an interpreter.

Here’s what’s so worrisome to the Yankees’ brain trust. Tanaka gambled on rehab over surgery last summer, convinced he could soldier on despite the injury. Now it’s too late to turn back. Tanaka has to keep pitching until the ligament ruptures – unless, of course, he’s worried about just that and intends to finesse his way through 30 starts.

That would explain the disappearing heat. Of those 26 fastballs, only three were four-seamers, the rest were sinking two-seamers. Put it this way – the two-seamer is his new fastball, as it appears hitters no longer have to worry about being blown away by the 95-96 mph nuclear heat Tanaka summoned on demand before he got hurt.

On Monday, he maxed out at 93 mph twice but otherwise averaged 91 mph. Those are still respectable radar-gun readings, and the splitter and slider remain effective. But that’s not enough to get swings and misses more than one time through the order — not in the AL East and especially not against Toronto or Boston.

Don’t underestimate the trickle-down effect of Tanaka’s demotion from untouchable ace to someone now vulnerable to big innings. Michael Pineda has to become the de facto ace for the Yankees to be competitive in the division; he hasn’t thrown a full season since 2011. CC Sabathia has to be perfect on the corners if all he has is an 88-91 mph fastball and an arthritic knee. And Nathan Eovaldi has to prove he can coexist with an impatient fan base in the Bronx.

You could hear the uncomfortable murmuring in the stands as Tanaka came apart during the Jays’ five-run third inning. He was nearly flawless until that point, retiring six of the first seven batters he faced, including three strikeouts. And the afternoon itself was like a gift from the fates – brilliant sunshine, a warm ovation for Joe Torre as he threw out the first pitch, and all the good will and optimism that rides shotgun on a home opener.

The vibe wasn’t just positive, it was practically euphoric, at least until Tanaka’s issues were put on full display in the third inning. Kevin Pillar singled to left, No. 9 hitter Devon Travis drew a five-pitch walk and, with the top of the order coming up, the Jays already had collected enough data to realize this wasn’t the 2014 Tanaka they were facing. This was a diluted version, missing precious velocity, about to get ambushed.

“We made some adjustments,” is how Toronto manager John Gibbons described his hitters’ revamped approach. A year ago, opponents had to defend against Tanaka’s rising four-seamer, leaving them vulnerable to the devastating drop of his splitter.

Up or down in the strike zone — a hitter has to make his choice, he can’t cover both. That’s why Tanaka was such a beast; he could beat you in either quadrant. But not in 2015. Russell Martin punched a two-run single to right, giving Toronto their first lead, followed soon after by Edwin Encarnacion’s massive two-run HR to left off a 90-mph sinker that barely moved.

By the fourth, Tanaka had lost his fastball altogether. With a 1-2 count on Martin, the right-hander threw six straight off-speed pitches to register a strikeout. But the damage had already been done, and the Jays had already tucked away the data on the Yankees’ damaged ace.

“The more you see [Tanaka], the more you can get a sense of how he works,” Gibbons said. “It’s no secret his velocity is down; anyone who doesn’t have that extra [velocity], you don’t have to commit as early. It gives you more time.”

That’s the kind of scouting report that could undermine the Yankees’ chances in the East. Without

Tanaka – or even with him with No. 3-type stuff — they’re just another team. No real stars, no real buzz, not much except a long-shot prayer that everyone stays healthy. Most of the sellout crowd, in fact, had already bailed by the time Didi Gregorius put the finishing touch on a dismal afternoon by getting thrown out trying to steal third in the eighth, ending the inning. With the Yankees down by five runs, it was an unforgivable mistake.

“Hopefully it’s something that never happens again,” said Joe Girardi, willing to assume the kid shortstop will be smarter in the future. True or not, there are bigger issues looming for the Yankees and Tanaka, both of whom ended the day needing a strong dose of amnesia.