It sounds trite to say that everything was going so well, but … everything was. The Braves had lapped the field in the National League East and were in Position A to finish the regular season with baseball’s best record, and best of all, a long-sputtering lineup was sputtering no longer. This was due in large measure to Jason Heyward, pressed into service as a leadoff man because nobody else fit the bill.

On its face, Heyward batting first seemed an even bigger misfit. At 6-foot-5 and 240 pounds, he’ll never be confused with Maury Wills. But baseball, as we’re constantly reminded, is a funny game, and sometimes the strangest combinations yield the sweetest results.

On July 27, the day Fredi Gonzalez decided to write Heyward’s name atop his lineup card, the Braves were 58-45, having gone 45-43 since their 13-2 start. Heyward was batting .223 with an on-base percentage of .325. The Braves are 19-4 since, Heyward having hoisted his average to .253 and his OBP to .347. Maybe this grand surge hasn’t all been because of one flick of a pen — masterful pitching has, we must concede, had much to do with it — but this team has been better with Heyward leading off than with anybody since … Rafael Furcal? Otis Nixon? Brett Butler?

Everything was going so well, and then the left-hander Jonathon Niese threw an inside fastball too far inside in the sixth inning of Wednesday’s game in New York. We can discern from Niese’s rueful reaction that he had no intention of plunking Heyward. A pitch got away, as pitches sometimes do. This fastball, clocked at 90 mph, smacked into Heyward’s jaw just under the flap of his helmet. An inch higher and he might have been left with nothing more than a sore ear. Four hours later came a rather different diagnosis: fractured jaw; out four to six weeks.

The Braves will still win the East and make the playoffs, and even a six-week absence would mean that Heyward might be able to play in Round 1. What’s unknowable today is how effective he’ll be after this latest enforced layoff. It took him a while to find himself after returning from the appendectomy of April, when he missed only 3 1/2 weeks. How will he be after having a jaw broken in two places and surgically repaired? How long before he can eat solid food? How long before he’s in game condition? How long before the catalyst can again be catalytic?

If there’s a sliver of good news amid this deflation, it’s that Heyward hasn’t been ruled out for the duration. He figures to be back at some point. But the past four weeks have served to underscore how gifted and important he is, which makes his loss doubly galling. In the 21 games he started since July 27, he reached base in all but one, and the exception came on a night when he left after an inning with a neck spasm. (Technically he reached Wednesday, although he never made it to first base.)

Jordan Schafer, who’s back from an injury of his own, can bat leadoff in Heyward’s stead, and Schafer has had a nice enough season. But he’s not the player Heyward is, and the absence of Heyward in right field surely will mean more playing time for B.J. Upton, who hasn’t had a hit in two weeks. It’s possible the absence of outfield options will force Gonzalez to keep playing the elder Upton until he does something good, but that assumes he ever will.

Recent postseasons have proved that it doesn’t much matter how you get there as long as you do. Still, the Braves — the best home team in either league — would rather be the No. 1 or No. 2 seed and have a home-field edge in the Division Series than the No. 3. As of 8 p.m. Wednesday, they led the Pirates by 2 1/2 games and the Dodgers by 3 1/2. (Owing to head-to-head records, they hold the tiebreaker over both.) Losing Heyward will make the chase for the league’s best record more problematic, which isn’t to suggest the Braves are doomed. They’ve withstood more than their share of knocks to get to 77-49. They aren’t apt to collapse now.

That said, we return to our original premise: Over the past four weeks, everything had gone so well as to make us begin to believe in a way we haven’t believed in any bunch of Braves since Jim Leyritz turned on Mark Wohlers’ slider. This October would be different, we were starting to tell ourselves, because these Braves are different. And they still might be. Jason Heyward’s broken jaw doesn’t mean these Braves can’t win the World Series. It does, however, complicate the process.