When manager Joe Girardi opted to start Masahiro Tanaka on Friday night on four days’ rest instead of the usual five he provides the Yankees’ ace, the manager never publicly said the move was made with the Blue Jays in mind.

Nevertheless, it was very clear by using Tanaka against the Mets in the first of three Subway Series games at Citi Field, Girardi was preparing to use him again Wednesday night in Toronto.

It was a good plan because the Yankees are chasing the Blue Jays in the AL East and open a critical three-game series Monday night at Rogers Centre.

But in the wake of the Yankees and Tanaka getting beat, 5-1, while the Blue Jays kept rolling past the Red Sox, Girardi might be wise to not start his best pitcher on four days’ rest on Wednesday.

Instead, Girardi should begin lining up Tanaka up for the Oct. 6 wild-card game because it is becoming very clear the Yankees aren’t going to win the East.

The Yankees enter Saturday’s matinee a season-high 4 ½ games back of the Blue Jays with 15 games remaining. The Blue Jays’ magic number to clinch the title is 12.

“If they wanted me to go in five days, I’d be ready to go,’’ said Tanaka, who exited after six innings for pinch-hitter Jacoby Ellsbury having thrown 82 pitches. That is the fewest pitches Tanaka has thrown since Aug. 9 (seven starts) when he left after 80.

As for starting Tanaka on Wednesday against the Blue Jays, Girardi wasn’t ready to say.

“We will see how he is in a couple of days and go from there,’’ Girardi said.

Working on four days’ rest for the second straight time and fifth this season, Tanaka was bitten by the home run. Tanaka entered the game having surrendered 22 homers, which was the ninth highest among AL pitchers with at least 100 innings pitched.

“I thought he threw the ball well,’’ Girardi said of Tanaka. “He made two mistakes, a splitter up and a slider that backed up.’’

Lucas Duda crushed a 1-2 splitter clocked at 89mph far over the right-field wall in the second for a 1-0 lead. After leaving two runners on in the fourth and working a perfect fifth, Tanaka watched Daniel Murphy scorch a 2-2, 85-mph slider beyond the right-center field fence.

In six innings Tanaka gave up two runs, five hits, didn’t issue a walk and fanned four. He is 12-7 after entering the game 3-0 with a 2.54 ERA in his previous three outings and is 8-3 with a 3.01 ERA in his last dozen starts.

“He pitched well enough to win the game,” catcher John Ryan Murphy said. “The two mistakes cost him.”