BALTIMORE — The notion that the Boston Red Sox have the best starting rotation in baseball is soooo last year.

To be more specific, it’s so December 2016. That’s when GM Dave Dombrowski swung a blockbuster deal that brought White Sox ace Chris Sale to Boston for a change of hosiery. At the time, the trade — which sent top Boston prospects Yoan Moncada, Michael Kopech and two other players to Chicago — was widely considered to have given the Red Sox the stoutest starting five in the majors.

Rick Porcello was coming off a Cy Young season. Although David Price had a down year for him, he was still:

(A) A 17-game winner

(B) A fellow Cy Young winner

(C) David Price

Those two combined with Sale would comprise the baddest big three in the bigs. Or so went the thinking. On top of that, the Sox had knuckleballer Steven Wright (an All-Star last season) and deadline darling Drew Pomeranz bringing up the rear of the rotation. Not too shabby.

Six months later, things look decidedly shabbier. Oh, Sale has been every bit as good as advertised, leading the majors in strikeouts and tying his own record by tallying double-digit K’s in eight straight starts. But after that, it’s been one big game of Whack-A-Mole.

For openers, Price spent the first two months of the season on the disabled list with an elbow strain. Then, in early May, Wright joined him on the DL with a sprained knee that resulted in season-ending surgery a couple of weeks later. Although the Red Sox finally got Price back earlier this week, on Friday they lost Eduardo Rodriguez — the young lefty who’d been a godsend to Boston’s reeling rotation — to a knee injury that he sustained when he … wait for it … slipped off the bullpen mound while warming up prior to Thursday’s series opener in Baltimore. As if that weren’t enough, Porcello is dealing with a nasty Cy Young hangover that continued on Friday night against the Orioles.

The 28-year-old righty started off the game by serving up a leadoff long ball to Seth Smith. Two batters later, Manny Machado became the first player since Mark Reynolds in 2011 to hit a home run into the upper deck at Camden Yards. Even though Porcello settled down and managed to last six innings, he was almost at a loss for words after the game.

“Definitely not how you want to start off,” he said quietly, standing in the visitors clubhouse following a 3-2 loss that allowed Baltimore to leapfrog Boston in the AL East standings and move into second place behind the Yankees. “Got to be better early on, be sharper. That’s the bottom line. Giving up too many hits, too many baserunners.”

That has been the story all year for Porcello.

Entering Friday’s action, opponents were hitting .307 against him. That was the fourth worst mark among American League starters, and 77 points higher than last year. After allowing eight hits and a walk against the Birds, his WHIP now sits at 1.48, way up from 1.01 a year ago.

“To be honest,” John Farrell said, “he’s a little snake-bit.”

The same could be said of Red Sox fans in the wake of the Rodriguez news.

Through the first two months of the season, the 24-year-old southpaw was the best Boston starter not named Chris Sale. Suddenly, the Red Sox will be without Rodriguez for who knows how long.

“I don’t have a time frame on when he’s going to be able to get back on the mound right now,” Farrell said before Friday’s game, “but we’re hopeful that this is on the short end.”

The good news is, thanks to an off-day following the weekend series in Baltimore, the Red Sox simply can skip Rodriguez’s next turn in the rotation and keep their other starters on regular rest, which is probably what they’ll do. But after that, they’ll have to figure something out. Lefty Brian Johnson, who shut out the Mariners in May but got hit hard by the Blue Jays in his only other start, is the most likely option.

On the one hand, Johnson is a former first-round pick. On the other hand, he’s 26 and is pitching in Triple-A for a third straight year, which begs this question: Can the Red Sox, who were a preseason favorites to play deep into October, deliver on their promise given the current state of their starters? Maybe.

But it sure would be easier if they had the best rotation in baseball.