The Mets' Pete Alonso wears a smiles as he heads...

The Mets' Pete Alonso wears a smiles as he heads to the dugout after scoring on a double off the bat of Robinson Cano during the first inning against the Reds on Sunday in Cincinnati. Credit: AP/Gary Landers

CINCINNATI — Pete Alonso keeps making history, and this time he surprised even himself.

His double in the first inning of the Mets’ 6-3 win over the Reds on Sunday gave him 30 this year. He is the first rookie in MLB history with 30 doubles and 50 homers.

The Yankees’ Aaron Judge, the only other rookie to reach 50 home runs, had 52 homers and 24 doubles in 2017.

“That’s really cool. I didn’t know that,” Alonso said. “I thought Judge had 30 doubles, but that’s pretty cool. I didn’t know that. That’s awesome.”

With Judge’s rookie homer record within reach, Alonso (50 homers) wants to finish strong in his historic debut season. The likely National League Rookie of the Year has seven games remaining in the regular season.

“It would mean a lot to finish strong and keep pushing,” Alonso said. “I like to do everything 100 percent. I’d like to end the year how I’ve been all throughout. I don’t want to have a sour taste in my mouth, knowing I could do more.”

Playing a sixth full month for the first time (the minor league season ends around Labor Day) has been difficult, Alonso said. He noted that in years past, he went to the instructional league or the Arizona Fall League, so it’s not that different.

“I feel like my body is holding up really, really well,” he said. “I’ve also done a really good job of training and preparing in the offseason, getting my body ready for it. Because ultimately, this is where I wanted to be and I wanted to be in the best possible shape coming into this year.”

Gsellman’s next step

Robert Gsellman (partially torn right lat) is scheduled to throw live batting practice Monday afternoon at Citi Field, a step forward after his recent bullpen sessions.

Always confident, Gsellman, who will pitch to teammates, joked that he plans to “carve them up like turkeys on Thanksgiving.”

Extra bases

Robinson Cano left the game after getting hit by a pitch. X-rays of his left big toe were negative. “It’s a little sore,” manager Mickey Callaway said, adding that Cano might be out of the lineup Monday with the Mets due to face a lefthanded pitcher (the Marlins’ Caleb Smith) .  .  .   J.D. Davis’ homer was his 20th of the year. The Mets have five players with at least 20, a franchise record .  .  .   Alonso can thank Mets pitchers for the assist in his pursuit of the home run title. They held the Reds’ Eugenio Suarez (second in the majors with 48 homers) to 3-for-12 with no homers this series.