WASHINGTON — The Mets have at least kept it interesting into September.

By that we don’t mean playoff-race-interesting, but still worth a watch. With 3 ½ weeks remaining until they likely play their final game of 2023, here’s a guide to what is keeping the Mets watchable:

It took until Tuesday for the Mets to get their rookie quartet of Francisco Alvarez, Brett Baty, Mark Vientos and Ronny Mauricio in the starting lineup together.

How often will we see that foursome in the lineup over these final 3 ½ weeks?

Wednesday offered a reminder of the different factors at work, as Alvarez was on the bench against the Nationals though he had hit a three-run homer the previous night.

The Mets have been cognizant of Alvarez’s workload and are looking to keep the rookie catcher fresh over this final stretch.

Manager Buck Showalter also admitted he’s walking a tightrope trying to get playing time for the rookies and putting his best team on the field for the integrity of the playoff races.

“It’s a challenge, because I am trying to be fair to the teams that are counting on us to play,” Showalter said before the Mets’ 3-2 loss to the Nationals. “If you look at our schedule the rest of the way, just about all [opponents] are in it, unless something changes. But the tiebreaker is always going to be what’s best for the Mets and our players, so you are trying to do a little bit of both as much as you can.”

Pete Alonso has hit three homers in his past three games, bringing his season total to 42. Matt Olson is the MLB leader with 46 and Shohei Ohtani is next at 44. Kyle Schwarber was right behind Alonso with 41.

A month ago, the idea of Alonso having a shot at the MLB home-run crown didn’t seem great, but with 11 homers in 28 games, the Mets first baseman had become a factor.

Alonso wore the crown in 2019, when he established a rookie record with 53 homers. There’s no reason to doubt his chances of reaching 50 this season and maybe finishing first again.

The Japanese right-hander has taken the baton from Jacob deGrom as the starting pitcher whose turn in the rotation elicits excitement.

Once upon a time, there was Matt Harvey day, followed in more recent years by deGrom day. Now it’s Senga day.

Senga’s next turn is Friday night at Minnesota, where he will look to follow the dominant start he had against the Mariners, in which he tied a career-high with 12 strikeouts.

After pitching to a 2.68 ERA in his nine starts since the All-Star break, Senga has essentially answered the question (in a positive manner) of whether he’s capable of leading a rotation.

The optics of Edwin Diaz now traveling with the Mets suggest the All-Star closer will get to pitch this season if he reaches the prescribed benchmarks in his rehab from patellar tendon surgery.

Diaz entering to Timmy Trumpet’s “Narco” during the final homestand of the year would be a feel-good moment in an otherwise lost season for the Mets, but that is provided there isn’t even a shred of doubt he is ready physically.

Otherwise, Diaz can wait until the Grapefruit League begins in February to start showing he is back.

DJ Stewart has been a terrific second-half story for the Mets as a player who has emerged from nowhere to possibly position himself for a roster spot next season.

Stewart has nine homers since Aug. 15, which is tied for fourth in MLB over that span.

Even if he doesn’t fit, watching Stewart finally reach his potential — he was a first-round draft pick by the Orioles in 2015 — has added some flavor to this final stretch.