Five months ago, the Phillies and Diamondbacks played three games in Philadelphia and never separated by more than one run.
Arizona won two of them.
Nobody knew then that those three April afternoons might become a preview of September.
The Phillies open a three-game series Monday night at Chase Field at 77-60, tied with Chicago for the best Wild Card record in the National League. Arizona enters at 73-65, holding the final playoff position by only a half-game over San Diego.
So forget the calendar for a moment.
This series has leverage.
The Phillies can leave Phoenix having shoved one of their closest pursuers farther down the standings. Or they can allow the Diamondbacks to turn what currently looks like breathing room into another crowded Wild Card race.
That is what September does to baseball games.
It changes their weight.
Philadelphia arrives in Arizona having played its best month of the season. The Phillies went 20-7 in August after stumbling through a 9-15 July. They have won 13 of their last 15 and swept the Angels over the weekend, their fourth three-game sweep of August.
The question now is whether August was a turnaround or merely a hot month.
Arizona gets the first crack at answering it.
There is something fitting about that.
When these clubs met at Citizens Bank Park in April, the Diamondbacks won the opener 5-4. The Phillies took the middle game 4-3. Arizona won the finale by that same 4-3 score.
Three games.
Three one-run decisions.
Arizona left Philadelphia with the season-series advantage, 2-1.
Now every one of those margins feels a little more familiar.
The Phillies have spent much of this season living in close games. They enter the series 23-11 in one-run contests. Arizona has played plenty of them, too, and Chase Field has hardly been an easy destination: the Diamondbacks are 40-29 at home.
Monday's pitching matchup only adds another layer.
Aaron Nola enters with an ugly season line — 5-10 with a 5.03 ERA — that disguises how much better he has pitched recently. Over his last six starts, Nola is 2-2 with a 2.60 ERA. He allowed two runs over six innings against Seattle in his most recent outing.
Across from him will be Brandon Pfaadt, who has quietly become one of Arizona's steadiest pitchers.
Pfaadt is 7-1 with a 3.51 ERA overall. More importantly, he has gone 7-0 with a 2.15 ERA over his last 11 starts.
That is not exactly the soft entry into September the Phillies might have ordered.
Neither is the expected return of Ketel Marte.
Marte is eligible to rejoin Arizona on Monday after an absence that included time on the restricted list following an unexcused absence and then the injured list because of left knee inflammation. Whatever questions remain around the circumstances, the baseball part is simple: Arizona expects to get back a three-time All-Star who has 21 home runs and 67 RBIs this season.
That matters for a Diamondbacks team that does not have much room for a prolonged stumble.
Neither do the Phillies.
Yes, Philadelphia owns a 4½-game advantage over Arizona. Yes, it has finally created some distance from the playoff cutoff.
But look beyond Phoenix.
Atlanta comes to Citizens Bank Park for four games immediately after this series. Houston follows. Then the Phillies go to Atlanta for three more.
There is no portion of the schedule where Philadelphia can reasonably plan on correcting September mistakes later.
That is why these three games feel different.
A month ago, the Phillies were trying to get themselves back into comfortable playoff position.
Now they can begin making somebody else uncomfortable.
Take two of three in Arizona and the Diamondbacks leave the series at least 5½ games behind Philadelphia. Sweep, and the gap becomes daunting with only a few weeks remaining.
Lose two or three, and Arizona is suddenly close enough to make every glance at the scoreboard matter again.
That's the opportunity the Phillies earned with their August.
Not merely to occupy a playoff spot.
To defend it.
And the first team standing in the way happens to be the same one that showed them in April just how little margin there can be between winning a series and losing one.
Back then, one run decided everything.
In September, one game can start to feel the same way.
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