Amid the Red Sox’s myriad problems, Chris Sale might be at the top.

The Boston ace fell to 0-3 — with 13 runs allowed in 13 innings — with his latest shelling coming Tuesday in the Red Sox’s home-opening 7-5 loss to the Blue Jays. Sale was asked afterward if he had ever felt this lost in his pitching career.

“Never in my life,” the lanky lefty said, according to MassLive.com. “But that’s not going to stop me. I don’t have an inch of back-down in me. I never will. Never give up. Just gotta keep fighting.”

Sale, 30, is coming off a season in which he had two stints on the disabled list due to shoulder issues, but that did not stop the Red Sox from plowing ahead with a five-year, $145 million extension this offseason.

“If I knew what it was I’d fix it,” Sale said. “That’s kind of where I’m at. I’m spinning my tires looking at this, looking at that. See if I’m tipping pitches. See my mechanics. See if it’s this, if it’s angles. I’m still searching. I’ll find it. I know who I am, what I can do. I’ve been there before. I’ll keep grinding.”

Sale is only one-fifth of the problems in a Red Sox rotation that has an 8.78 ERA and a 3-9 team that currently sits in last place in the AL East.