Pete Alonso's walk-off HR completes Mets' sweep of Nationals

The Mets are about to learn a lot about who they are.

They beat the Nationals twice, 4-1 and 5-4, on Thursday to sweep the doubleheader and the series, Pete Alonso’s walk-off home run in the second game punctuating the team’s big-time rebound — a revival, perhaps, after its worst run of the year.

But now comes the hard part, a potentially season-defining stretch: 13 consecutive games against the Dodgers and Giants, powerhouses from the NL West.

Los Angeles, the defending World Series champion, visits Citi Field this weekend. After the Mets get lefty 13-game winner Julio Urias on Friday, they will see two of the Dodgers’ aces: Walker Buehler and his NL-leading 2.13 ERA on Saturday, then the newly acquired Max Scherzer on Sunday.

The Mets enter these critical two weeks at 59-55, a half-game behind the Phillies in the NL East. They have won three in a row but just five of their past 14.

These games won’t be quite the same as the others this week.

"Yeah, these games are really important," Alonso said. "But this is a show-me stretch. What are we made of?"

Added Brandon Nimmo: "If you want to be a playoff team, you have to beat some other playoffs teams. These two teams are very, very good. They obviously have very good records and very good track records of success. This series, these next few series, will be good tests of playoff baseball."

The Mets feel ready for such tests after their offense showed signs of competency against Washington (50-65). They pounded out 22 hits in 13 turns at bat Thursday.

Michael Conforto had two hits in each game. Jonathan Villar, filling in at shortstop for the injured Francisco Lindor and sort-of-injured Javier Baez, went 4-for-6 with his third homer in six games.

Alonso’s hit was the biggest. After Trevor May and Jeurys Familia combined to blow a three-run lead in the seventh and final inning, Alonso walloped a skyscraping homer off newly named closer Kyle Finnegan.

"That’s how we’re supposed to swing the bat," manager Luis Rojas said. "I’m just glad we’re doing it game to game. It’s not just showing up one game and then it disappears."

In the opener, Nimmo homered and drove in all four Mets runs — with a three-run home run pulled to rightfield in the second and an RBI single slashed down the leftfield line in the fourth.

"You love to have games like that, where you’re carrying the load," said Nimmo, who was 0-for-4 in the second game. "Because there’s plenty of games like this last one, where you didn’t carry any load."

Marcus Stroman held the Nats to one run and three hits in 5 1/3 innings, striking out eight and walking two. That lowered his ERA to 2.79. He has completed six innings in just one of his past 10 starts.

His only issue this time was the heat and humidity — conditions that, later in the day, inspired a cheer from the Citi Field crowd when a cloud briefly blocked the sun.

Stroman said that in the top of the fourth, after fielding Juan Soto’s weak ground ball, he became "super lightheaded" and needed a moment to "get back to seeing straight." Rojas, pitching coach Jeremy Hefner and an athletic trainer visited him on the mound. They brought him a bottle of water.

"I’m not someone who hydrates very well," Stroman said. "It’s still something I’m trying to learn to do better on game day . . . I get so nervous it’s hard for me to put anything in my system on game day."

Said Rojas: "He’s known to sweat profusely on days like this."

Nationals starter Sean Nolin, a Seaford native pitching in his first major-league game since 2015, allowed four runs in three-plus innings.

Making his Mets debut the second game, righthander Trevor Williams allowed one run in 4 1/3 innings. Back-to-back doubles from Conforto and J.D. Davis put the Mets on top in the fourth. Villar added a two-run dinger in the sixth.

The wins meant positive momentum as the Mets head into an immediate next challenge.

The Dodgers have outscored opponents by 181 runs, the Giants 136. The Mets, for reference, are at -13.

"These two teams, we’ve paid attention from afar," Rojas said. "I don’t think we shy away because of the talent or the run differential you may see in the standings, which is unbelievable."