ST. PETERSBURG, Fla. — Count the scouting fraternity among those who are confused why Masahiro Tanaka has been as hittable as Iron Mike.

“When spring training ended he looked like he was back to before the injury,’’ said a scout who watched the Rays pummel Tanaka for six runs and nine hits (three homers) in a 9-5 loss Saturday. “Now he doesn’t look the same.’’

Looking at his last four starts, and certainly the last two, Tanaka no longer holds the mantle of staff ace. In those four games, he is 2-2, but has allowed 34 hits in 18 innings, given up 10 homers, has a 10.50 ERA, hitters are batting .395 and have an OPS of 1.260. Overall, Tanaka is 5-3. His 6.56 ERA is 86th out of the 88 AL starters who qualify for the ERA title.

“He isn’t finishing his pitches, and he’s making mistakes with the fastball,’’ said another scout at Tropicana Field over the weekend.

Following Saturday’s debacle, pitching coach Larry Rothschild said it was time to go back to “square one’’ with Tanaka, whose next start is Thursday against the woeful Royals.

“The first thing is that we have to get consistency out of his pitches. He has to have his consistent split and consistent slider. If he has those two things, he’s going to be successful,’’ Joe Girardi said. “It becomes frustrating for a player who is used to having a ton of success when you struggle. This is the first time he’s struggled here for a length of time. It becomes frustrating and sometimes you can try to change this, change that. Let’s get back to what made you successful. To me, that is always square one.’’

Saturday, Tanaka switched where he started his windup from the first-base side of the pitching rubber to the third-base side and was shelled.

“We have to get his stuff right, first and foremost, and go from there,’’ Girardi said.

When Tanaka pitches like he did on April 27 at Fenway Park, where he threw a three-hit, complete-game shutout against the Red Sox, nobody mentions his right elbow history. When he hits the skids like he has in the past two starts, the minor tear in the right ulnar collateral ligament suffered in 2014 becomes a topic.

Yet, the Yankees follow Tanaka’s workouts in between starts and don’t see a sign of injury to any body part.

With Tanaka turning in a bullpen-killing performance Saturday and the Yankees in a stretch of 20 straight games and the starters averaging less than five innings in the previous 10 games, the Yankees elevated right-hander Bryan Mitchell from Triple-A Scranton/Wilkes-Barre Sunday.

Mitchell opened the season with the Yankees and was sent to SWB after nine relief outings. In three starts for the RailRiders, Mitchell was 0-1 with a 4.00 ERA.

“He’s been pitching better of late and he is a guy who can give you nearly 70 pitches in a bullpen that’s fairly taxed,’’ Girardi said. “We need for him to step up for us.’’

Mitchell last pitched for the RailRiders on Tuesday.

To make room for Mitchell, the Yankees optioned right-handed reliever Giovanny Gallegos to SWB.

According to Girardi, first baseman Greg Bird will begin baseball activities Monday at Yankee Stadium.

“The reports we have been getting from home this week have been really good,’’ Girardi said. “The old dreaded tee-and-toss should start on Monday.’’

Bird went on the DL May 2 with a bruised right ankle. He is hitting .100 with a homer and 6 RBIs.

On the DL since May 13 with an inflamed rotator cuff in the right shoulder, Aroldis Chapman will be looked at Monday by a doctor.

“We will see exactly when they will start his throwing program,’’ Girardi said.

After taking a wicked foul tip off the mask in Saturday’s game that landed on the right side of his jaw, Gary Sanchez was in Sunday’s lineup.

“I wasn’t really as worried about a concussion as his jaw,’’ Girardi said Sunday. “He says he’s OK, and we continue to watch him.’’

Sanchez went 0-for-4 with a walk, a throwing error and didn’t run hard to first when he hit into a double play in the fifth inning Sunday.

Yankees batters whiffed 17 times to tie the franchise’s record for most strikeouts in a nine-inning game that was set April 15 against the Cardinals. Including extra-inning games the Yankees are 4-1-1 all time when striking out 17 times or more. Matt Holliday, Starlin Castro and Aaron Judge went 0-for-12 with 11 strikeouts. Holliday and Judge fanned four times each; Castro three. … Girardi had arthroscopic right knee surgery on last Monday’s off day.