OAKLAND -- Blue moons are a rare natural phenomenon. Two or three years can go by without seeing two full moons in the same calendar month, inspiring the idiomatic expression "once in a blue moon."

Even rarer than a blue moon may be a rough start from Mets ace Jacob deGrom.

The Mets fell to the A's, 10-4, in Saturday's matinee at the Coliseum, evening the series ahead of Sunday's rubber game. New York's lead in the NL East dropped to 1 1/2 games over Atlanta, and the magic number to clinch the division remained at nine.

It's rather unusual to see deGrom credited as the losing pitcher in a blowout Mets loss. The 34-year-old righty was not sharp in his first career start at the Coliseum, snapping his MLB-record streak of 40 games with three or fewer earned runs allowed that dated back to Sept. 3, 2019.

That streak was history after the A's stunned deGrom with a four-run first inning, but it didn't end there. Oakland added another run in the third when center fielder Seth Brown took deGrom deep to center, capping the upstart A's five-run outburst against the two-time Cy Young Award winner.

"It's tough to see him have one of these kinds of days," said Jeff McNeil, who went 2-for-5 at the plate but misplayed a first-inning fly ball that resulted in a two-run double for the A's. "But he's one of the best pitchers in the world. He's going to come back next time and give us a good game."

deGrom had not allowed five or more runs in a start since May 17, 2019, when he was tagged for seven runs (six earned) over five innings in an 8-6 loss in Miami.

Once in a blue moon? That's about right. There's been one blue moon since the last deGrom start that could reasonably be called a clunker.

"It's frustrating," deGrom said. "I've done it before. I think almost everybody who's pitched has probably done it before. You try to avoid those, but I wasn't able to make the adjustment and figure out how to get those guys out."

The A's offense didn't make a lot of noise against Mets pitching in the series opener, but they came out swinging the next day. Oakland batters notched a season-high six hits against deGrom and didn't slow down when he exited the game after four innings, picking up 14 knocks on the day.

"He’s a strike thrower: come out swinging. Obviously, there’s a balance to that," A's manager Mark Kotsay said of Oakland's strategy vs. deGrom. "But we felt the game plan was right and kept swinging. Overall, you look at the day, and those are probably the best at-bats we’ve taken throughout a game, and it couldn’t have come at a better time.”

The swings the A's didn't take were equally notable. Entering the day, deGrom had issued just four walks in nine starts this season. He doubled his season total on Saturday, giving out four free passes to A's batters. 

Two of the batters deGrom walked came around to score in that four-run first inning.

"We go out and put up three in the first, and then to go out and give up four right away is unacceptable," deGrom said. "Four walks, just all-around unacceptable and a terrible job by me."

Over deGrom's elite nine-year career in New York, the right-hander has set an extremely high standard of performance, one that Mets manager Buck Showalter said has "spoiled" the team. That's perhaps best demonstrated by the streak deGrom carried into Saturday. But every streak must come to an end at some point.

Players don't always perform as expected, Showalter said, especially when those expectations are set extremely high. deGrom manages to meet them the vast majority of the time.

"It reminds me, and should [remind] all of us, how hard it is to do what he does and the level he does it at," Showalter said. "I have an affinity for teams and players that do things that are expected. … It's so hard to repeat pitching at the level they are, hitters that hit .300 every year.

"It's so hard when everybody in the world is giving you their best shot. So, the reminder it is for me is the expectations [deGrom] creates by how good he is."

deGrom hasn't had to bounce back from a bad start in roughly three years, but he's ready to flush this one and get back to doing what he does best. After all, the next blue moon isn't expected for another year.