PHILADELPHIA — Noted philosopher William Nathaniel Showalter III assured us the sky wasn’t falling: It was just rain.

That observation from the Mets manager occurred four days before his team was set to break spring training without ace Jacob deGrom, who had been diagnosed with a stress reaction on his right scapula that morning and told to stop throwing.

Showalter further had to tweak his rotation after Max Scherzer’s right hamstring tightened, causing him to miss his final exhibition start.

A week into the regular season, the Mets are succeeding (with five victories in seven games) in no small part because of a rotation that has performed admirably, even without deGrom and with Scherzer pitching at less than full strength.

The early worries have shifted to the bullpen, which has created too much anxiety for Showalter. Thursday’s off day at least gives that unit a chance to reset following games the Mets lost Sunday and Monday in which they couldn’t protect leads. Turbulence with Sean Reid-Foley and Joely Rodriguez on Wednesday kept the game closer than it should have been in the Mets’ 9-6 victory over the Phillies.

But the Mets are headed to Citi Field for the home opener with a starting rotation that owns a 5-0 record and 1.29 ERA. Opponents have produced a paltry .437 OPS against the starting five. Taijuan Walker’s bursitis diagnosis that will cost him at least one start brings pause, but the initial seven games have brought renewed hope this group won’t only survive, but thrive. Especially following a three-game stretch against a scary Phillies lineup in which Walker/David Peterson, Tylor Megill and Scherzer combined to allow one run.

Scherzer allowed that run during a slog of a performance Wednesday that in some ways defines the pitcher the Mets signed to a three-year contract worth $130 million: a competitor who can beat you even with his B or C game.

There was a 29-pitch first inning in which Scherzer walked the bases loaded, but escaped unscathed. If that wasn’t taxing enough, he allowed hits to Nick Castellanos and Jean Segura leading off the fourth, struck out Didi Gregorius and Johan Camargo in succession and then surrendered an RBI single to Bryson Stott. The ensuing batter, Matt Vierling, maybe provided a favor to the right-hander by swinging at the first pitch and popping out.

Scherzer returned to the mound for the next inning and faced the All-Star cast of Kyle Schwarber, J.T. Realmuto, Bryce Harper and Castellanos. Only Realmuto reached base, on a single. The other three were retired.

“I think you see why a guy like [Scherzer] is in such demand,” Showalter said. “Especially the last inning, where he was in the batting order. That’s probably as impressive as you want to see. He just didn’t let it get away from him. He never gave in. He’s fun to watch compete.”

Then, laughing, Showalter added: “Not a whole lot of fun to think about taking him out of the game.”

Over his past 15 starts, Scherzer has pitched for three different franchises (Nationals, Dodgers and Mets), but there has been a constant: His team has won every time. In his last 21 starts, he is 13-0. Only two of those wins have come for the Mets, but it’s certainly a different dynamic than the team has encountered with deGrom, whose brilliance all too often has been wasted by underperformance elsewhere.

Scherzer noted this start felt different than his Mets debut on Friday in Washington in that his right leg was strong beneath him, the gimpy hamstring having vanished.

“I was throwing pitches where I kind of wanted, but they were just missing,” Scherzer said. “[But] I was making big pitches when I needed to, when runners were on base.”

If there’s been a silver lining to the deGrom injury it’s the Mets have gotten to find out about Megill, who otherwise would have been in the bullpen or relegated to starting at Triple-A Syracuse. After two superb starts from the right-hander, suddenly it’s fair to wonder if the Mets have found their next homegrown talent for the rotation. You wonder if Megill can join deGrom, Scherzer and Chris Bassitt to form a dynamic 1-4 punch.

But that’s a dream for another day, largely reliant on health. For now the Mets can just celebrate early signs the sky will remain above them, even without deGrom.

Any rain has come from Showalter picking up the phone to the bullpen.