WASHINGTON — To understand where the Mets are three games into this 2019 season, all you had to do was take a look at Pete Alonso as he got ready to make the trip to Miami for the second series of the year.

A white monogrammed handkerchief stood out in the left breast pocket of his suit jacket. It was a classy addition by the Mets rookie.

“That’s my grandfather’s handkerchief,” he said after the Mets’ 6-5 loss to the Nationals on Sunday on Trea Turner’s second home run of the game, a ninth-inning blast off Justin Wilson that allowed Washington to salvage the final game of the series. “My grandfather always felt that a lady should never have to carry her own handkerchief.”

Pete Alonso’s grandfather passed away this winter. His name was Peter.

This was Alonso’s way to honor his grandfather as he played the first three games of his career. His grandfather is with him in spirit and with the reminder of that white handkerchief.

It’s a small gesture, but it says much about Alonso and much about where the Mets are as a team and the position Alonso has established within the team.

The big first baseman picked up two more hits Sunday and is hitting .500 after his first series in the majors. He has shown class, talent and strength. He’s going to be all right. That’s how the Mets feel about their young players — and their team — after three games against their division rival.

They won two of three, and almost stole the third game Sunday, roaring back with three runs in the eighth to tie the game, 5-5, before losing in the ninth.

They will make mistakes, and you certainly will not agree with every decision made — like not starting Jeff McNeil after McNeil produced a four-hit game on Saturday or with keeping the lefty Wilson in the game when Jeurys Familia could have entered — but right now Mickey Callaway and Brodie Van Wagenen are testing the limits of their players to see what they really have.

Moments after Turner fast-twitched Wilson’s fastball into the left-field seats, Van Wagenen was on the elevator on his way to the clubhouse. “Great game, great weekend,” he said.

Before he got off, he made sure to shake hands and officially introduce himself to the elevator operator so next time the Mets are in town and the GM has to get to the clubhouse quickly, the operator will know immediately.

Van Wagenen is trying to build a certain culture here, and Alonso, McNeil and the players are aboard for the ride. McNeil had no qualms about sitting against left-hander Patrick Corbin. He came in the game defensively and struck out in the eighth.

The Mets are going into this as a team, and here is what this series told McNeil:

“This tells us we’re good and we’re deep,” McNeil said. “We’re going to fight back when we are down like we did today. We’re putting together good at-bats and the pitching looks good. I like what we see.”

After winning in the opener 2-0 behind their ace Jacob deGrom, the Mets pounded out 27 hits the next two games and scored 10 runs against the Nationals shaky bullpen, which could look to Craig Kimbrel for a boost.

Zack Wheeler surrendered a monster three-run home run to Turner in the third, when Turner ambushed a fastball. Other than that, Wheeler pitched well, and he too, came away with an appreciation for the Mets’ young players.

“A lot of the young guys are showing up at the plate, they are not scared,” Wheeler said. “A lot of times you see young guys come up and they are a little timid and stuff, but these guys are taking it by the horns and are going with it.”

Alonso is the most impressive of those players and came away with a .500/.571/.750 slash line this first series against top-of-the-line starters Max Scherzer, Stephen Strasburg and Corbin.

“I’m really happy with the way I am playing so far,” Alonso said.

Happy and proud. Just look at the handkerchief in his suit pocket.