“I was really spotting up my changeup,’’ said the 21-year-old lefthander from Mission, Texas. “It was a real big help throughout the whole game. It really made a big difference during the game, helping me keep the ball low and away. And that’s what I think I tried to maintain during the bullpen.

“And I was able to transfer it onto the mound during the game.’’

Although he recorded a no-decision in his previous outing May 3 (giving up a pair of runs on six hits in a 5-3 victory over Lexington), Pena was vastly improved Tuesday, combining with Hunter Cervenka and Tyler Lockwood for the first nine-inning no-hitter in franchise history, a 1-0 victory over the Rome Braves.

Pena earned the victory, which improved him to 2-2 on the season and lower his earned run average to a team-leading 1.72. He threw six perfect innings, striking out seven.

Keury De La Cruz gave Pena all the run support he needed when he hit a leadoff home run in the fourth.

As he stacked up one perfect inning after another, Pena said, he did not sense mounting tension in the dugout.

“I really tried to stay within myself and not try to do anything out of the ordinary,’’ he said. “Just keep it simple. Not put too much pressure on myself.

“As far as when the perfect game was going on, I wasn’t paying too much attention to that. I was just trying to go back out and repeat everything, inning by inning.’’

Pena was on a 90-pitch limit, and he was done after 83. He lobbied manager Carlos Febles and pitching coach Dick Such to leave him in for the seventh, but the pitch count trumped Pena’s desire for perfection.

“Yeah, actually coming out of the sixth, when I struck out the last guy, I had a good feeling about my pitch count and coming out for one more, especially with it being a perfect game,’’ Pena said. “But once [Febles] told me, I knew that was it. I guess I was on a pitch count.’’

Cervenka allowed one runner, on a walk, spoiling the bid for a perfect game, but he preserved the no-hitter and handed it over to Lockwood in the ninth. Lockwood picked up his second save of the season by retiring the side in order, striking out the last two batters.

“Coming on in the ninth, I don’t know if he had any pressure,’’ Pena said. “But I’m pretty sure if I came into a situation like that, with a no-no going, I’d have the butterflies going. But he really did a great job, just locking in, spotting up, and getting ahead of the hitters.

“It was just so surreal at that moment. Once we got in the clubhouse and we actually were told that we made history, that’s when it sunk in.

“I really can’t put into words how I felt, but it’s something that will be with me for a long time.’’

Pena was drafted by the Nationals (fifth round) as a high school senior in 2009 and by the Padres (13th round) in 2010 during his first year at San Jacinto (Texas) junior college, where he earned All-America honorable mention after going 10-3 with a 1.91 ERA.

But Pena waited to sign until he was drafted last year by the Red Sox (sixth round, 202d overall).

“It’s a wonderful experience playing for a wonderful organization,’’ Pena said. “I couldn’t be more blessed, especially down here in Greenville where we have a really nice stadium. It’s something you could really get used to, but our goal is to climb up the ladder.’’

Team effort

When Will Middlebrooks was promoted last week to Boston from Triple A Pawtucket, it affirmed all the hard work that went into scouting, drafting, signing, and developing the third baseman of the future.

“In scouting and development, there’s definitely some failure involved, even with the teams that are the best at it,’’ said Sox general manager Ben Cherington. “It’s not an exact science, and so when something does work out and you find someone who comes up and helps your team, it is gratifying.’’

Middlebrooks made a splash, getting extra-base hits in each of his first five games, including a grand slam last Sunday.

“There’s a lot of people who share in the credit for Will, starting with Will himself,’’ Cherington said. “But Jim Robinson, our area scout in Texas, first identified him and pushed us to draft him. Dave Finley [director of player personnel] was involved in cross-checking and seeing him a lot.

“Then certainly a lot of player development staff spent a lot of time with him. To Will’s credit, he was a really good athlete when we signed him, with good potential and what we thought was really a good makeup.

“But he’s turned himself into a good player. He’s matured as a person, so it’s great to see him come up and have success.’’

Power in Portland

Look for Juan Carlos Linares, the Cuban-born outfielder/designated hitter, to be on the move from Double A Portland. Linares is hitting .385 with 5 homers and 20 RBIs and leads the team with 11 multihit games. “At some point, we may try to get him to Triple A,’’ said Cherington. “We sent him to Double A simply because that was the best chance we could give him to get some more at-bats. He’s done really well.’’ . . . Portland righthander Stolmy Pimentel earned his first Double A victory in 18 starts Wednesday, allowing two runs on five hits in six innings in a 5-4 win over New Hampshire . . . Entering Thursday night’s game against Potomac, Single A Salem was leading the Carolina League in hitting with a team average of .287, which included a league-leading 76 doubles and nine triples. Outfielder Jackie Bradley led the team and was second in the league with a .378 average, while third baseman Travis Shaw ranked second on the team and third in the league at .375.

Michael Vega can be reached at vega@globe.com.