NEW YORK -- The loudest and longest ovation, of course, went to reigning National League Cy Young Award winner Jacob deGrom. Second-loudest? It may have been for rookie Pete Alonso, who elicited thunderous applause when he was introduced prior to the Mets’ home opener Thursday at Citi Field. A veteran of six career games, Alonso said he was “a little bit” surprised at the reaction, after a road trip that saw him hit .409 with a home run and seven RBIs.

“It’s my first day here, you know?” Alonso said. “Playing here at Citi Field and to be received like that, it felt really special to me. It’s much appreciated from the fan standpoint. Thank you to the fans.”

It wound up being Alonso’s least productive day as a big leaguer during the Mets' 4-0 loss to the Nationals; for the first time in a game he started, he went hitless. But that’s little worry to a Mets team -- and a fan base -- that can’t stop raving about its top prospect.

Alonso, in turn, is thrilled for the support. A total of 44,424 fans attended the opener, the second-largest regular-season crowd in Citi Field history. (First was on April 30, 2016, when the club gave away Noah Syndergaard garden gnomes.)

“I can’t wait to play the whole season here,” Alonso said. “This is exciting. It’s awesome playing here.”

Pomp and circumstance

The Mets’ pregame festivities for their home opener included moments of silence for Hall of Famer Frank Robinson, former pitching coach Mel Stottlemyre and longtime beat writer Marty Noble, who passed away March 24. The Mets invited Noble’s wife and daughters to visit the press box, where club officials left a bouquet of roses and a permanent plaque in his honor.

NYPD helicopters also performed a flyover during the national anthem, and Gil Hodges Jr. threw out the ceremonial first pitch to Mets legend Ed Kranepool.

Rotation swap

When the Mets broke camp, manager Mickey Callaway said he had no qualms stacking left-handers Steven Matz and Jason Vargas together in the rotation because of their differences in repertoire -- Matz featuring a mid-90s fastball, Vargas relying almost exclusively on pitches in the 70s and 80s. But after just one rotation turn, Callaway changed his mind, shifting Matz ahead of Zack Wheeler. Matz will now pitch Saturday against the Nationals; Wheeler on Sunday.

With off-days on Friday and Monday, the Mets could still skip Vargas, bringing deGrom back on five days’ rest for Tuesday’s game against the Twins. But Callaway said the team plans to keep Vargas on turn, resulting in two extra days of rest for deGrom.

Rearranging

As in Spring Training, the Mets issued David Wright’s old Citi Field locker to Robinson Canó, who has spoken often of his desire to be a leader in the clubhouse. Syndergaard also moved from his old corner locker to one in the middle of the room, which used to belong to Matt Harvey.

Standing firm

In a statement released Thursday, Mets broadcaster Ron Darling said he “stands by all recollections” that were written in his new autobiography, “108 Stitches,” which was released earlier this week. Former teammates have accused Darling of falsifying stories -- including Lenny Dykstra, who has threatened legal action. Darling said he will not comment further on the issue.