Francisco Álvarez also went deep, José Butto earned his first career win and New York handed the Diamondbacks a costly defeat as they try to maintain their slim lead in a crowded race for the final National League playoff spot.
Arizona stranded nine and hit into two inning-ending double plays with the potential tying or go-ahead runs at the plate.
"We've got to be a little bit more stubborn in some very key situations with men in scoring position and expect to execute at a very high level," Diamondbacks manager Torey Lovullo said.
Arizona leads Cincinnati by one game for the third NL wild card, with Miami and San Francisco 1 1/2 games back.
New York won hours after David Stearns agreed to become the team's president of baseball operations, according to several reports - filling a spot that's been vacant since Steve Cohen bought the team following the 2020 season.
Mauricio, who was called up from the minors Sept. 1 and began his career with a five-game hitting streak, put the Mets ahead 3-1 with a 440-foot shot deep into the second deck in right field in the fourth. The 22-year-old rookie flipped his bat high in the air and pointed to the home dugout before beginning his trot.
"You know that you hit it well and it just feels good," Mauricio said through a translator.
Mauricio has four RBI in the first two games of the four-game series.
"I expect a lot out of myself," he said. "I know that I'm a good ballplayer. And yeah, I expect for me to contribute."
One inning later, Diamondbacks left fielder Lourdes Gurriel Jr. didn't even move when Alonso hit a two-run drive that was clocked at 113 mph off the bat and traveled 424 feet into the second deck in left.
Butto (1-2) allowed one run and struck out seven in five innings. He threw 91 pitches, including just 25 in retiring his final eight batters.
"I spoke with Álvarez at that point and I said, We have to continue to attack hitters and get quick outs,'" Butto said through a translator. "Because in those first couple innings, I was going deep into the (count) and threw a lot of pitches there."
Sam Coonrod plunked Seby Zavala with the bases loaded in the eighth and then walked Geraldo Perdomo to make it 6-4 before Adam Ottavino got speedy Corbin Carroll to ground into an inning-ending double play.
"I thought it was a really good situation for us - we had the very top of the lineup coming up with the bases loaded and one out and we didn't execute. We didn't close the gap like I thought we would," Lovullo said. "I thought we were going to at least make it 6-5, put ourselves in position to play one run down in the ninth inning."
Ottavino closed out his 10th save with a perfect ninth.
Ketel Marte gave the Diamondbacks a short-lived lead with an RBI triple in the third. Gurriel added an RBI single in the sixth.
Ryne Nelson (7-8) gave up six runs in 4 1/3 innings.
The Diamondbacks recalled OF Jake McCarthy from Triple-A Reno and optioned OF Pavin Smith to the same affiliate.
Diamondbacks: Lovullo said C Gabriel Moreno's wife gave birth to a son. Moreno went on the paternity list Monday. ... INF Emmanuel Rivera (left shoulder) didn't play one night after banging his shoulder on the tarp trying to make a sixth-inning catch.
Mets: RHP Sean Reid-Foley (right lat) was placed on the injured list and RHP Reed Garrett was recalled from Triple-A Syracuse. Reid-Foley, who returned Aug. 23 after undergoing Tommy John surgery in May 2022, was injured at the end of his one-inning outing Monday.
The four-game series continues Wednesday night, when Mets LHP Joey Lucchesi (2-0, 3.54 ERA) will be called up from the minors to start against RHP Zac Gallen (15-7, 3.31).
Lucchesi is 0-2 with an 8.36 ERA in three starts for Triple-A Syracuse since his most recent start for the parent club on Aug. 18. Gallen threw the first nine-inning shutout of his career last Friday, when he held the Chicago Cubs to three hits in a 1-0 victory.
AP MLB: https://apnews.com/hub/mlb