NEW YORK -- The game-winning home run Oscar Hernandez hit Wednesday night represented an organization victory for the Arizona Diamondbacks. But as for the ball Hernandez hit? That was all his.

Hernandez hit his first major league home run leading off the top of the 12th inning Wednesday as the Diamondbacks edged the New York Mets 3-2 at Citi Field.

"It was awesome," Hernandez said. "This is the best feeling. I never felt (like this) before, honestly."

Opportunities like the one Hernandez had Wednesday night have been rare for the 23-year-old catcher, whom the Diamondbacks selected from the Tampa Bay Rays in the Rule 5 draft in December 2014. As a Rule 5 draftee, Hernandez -- who had not played above Class A in five seasons in the Tampa Bay chain -- had to spend the entire 2015 season on the major league roster. He ended up batting .161 in 18 games for Arizona after missing the first half due to a broken hamate bone.

Hernandez opened this season with Class A Visalia, for whom he hit .295 with three homers and 15 RBIs in 34 games before earning a promotion to Double-A Mobile. He was batting .196 with seven homers and 16 RBIs for Mobile when he was promoted to the Diamondbacks on Tuesday to replace starting catcher Wellington Castillo, who went on the paternity leave list following the birth of his son.

"Going to the minor leagues, that helped me a lot," Hernandez said. "I needed more experience. I (made) a big jump -- from low-A to the big leagues. It's different."

Hernandez was hitless in his first four at-bats Wednesday before homering down the left field line against Mets left-hander Jerry Blevins (4-2) . A Diamondbacks staffer retrieved the ball for Hernandez, who held the ball during a postgame interview session that included someone asking what he planned to do with the souvenir.

"That's going with me," Hernandez said with a wide grin as his hands closed tightly around and completely covered the ball. "This is mine."

The Diamondbacks' keepsake will be the progress Hernandez continues to make now that he's on a more traditional developmental path.

"It obviously feels good for 'Stew' (general manager Dave Stewart) and all our scouts who looked at him last year and during the Rule 5 draft," Diamondbacks manager Chip Hale said. "Having to hold on to him all last year and kind of missing a year, you're hoping he doesn't lose any development time. So it's been good for him."

Randall Delgado, the Diamondbacks' seventh pitcher, improved to 3-1 by throwing two perfect innings of relief as Arizona (47-66) won its third straight game and for the fourth time in five games overall.

The Diamondbacks led 2-0 entering the ninth, when Mets pinch-hitter Kelly Johnson hit a game-tying homer into the second deck in right field off closer Jake Barrett. But the ninth inning ended with Neil Walker (2-for-5) stranded at second and New York got just one runner beyond first base over the final three innings.

"That inning, I thought we were going to win the game," Mets manager Terry Collins said. "With the momentum, the energy, I thought we were going to get a base hit and win the game. We just didn't do it."

That has become a common theme for the Mets (57-56), who have lost four of five and are 10-18 since July 8 but remain just 2 1/2 games behind the Miami Marlins and St. Louis Cardinals in the race for the second National League wild card.

"We've been through these tough times," Collins said of the Mets, who were just 52-50 through July 30 last season before reaching the World Series. "But we're just not coming through when we need to as we did a year ago."

The Mets' comeback cost left-hander Robbie Ray, who allowed three hits and no walks while striking out four over seven innings, a chance to earn his first win since July 17.

Jean Segura went 3-for-5 with a walk and two stolen bases while scoring the Diamondbacks' first two runs -- the first on an RBI single in the third by Paul Goldschmidt and the second on a Goldschmidt sacrifice fly in the eighth. Goldschmidt finished 2-for-4 while Chris Owings was 3-for-5 with a stolen base.

Mets right-hander Bartolo Colon allowed one run on seven hits and one walk while striking out a season-high eight over seven innings. The 43-year-old Colon was trying to become the 18th pitcher to beat all 30 major league clubs.

NOTES: A spate of afternoon showers delayed first pitch by 20 minutes. ... The Mets selected the contract of INF T.J. Rivera from Triple-A Las Vegas and optioned OF Brandon Nimmo to the same affiliate. Rivera, a native of the Bronx, went 1-for-5 in his major league debut. To make room for Rivera on the 40-man roster, the Mets shifted 1B Lucas Duda (back) to the 60-day disabled list. ... Mets 3B Jose Reyes (oblique) is scheduled to begin a rehab assignment with Class A Brooklyn on Thursday. ... Diamondbacks OF Yasmany Tomas (stiff neck) missed his second straight game. ... Diamondbacks LHP Andrew Chafin (left shoulder) threw a scoreless inning Tuesday in his fourth rehab appearance for Class A Visalia.