Pena recorded a career-high 14 strikeouts and yielded two hits over six innings as the Class A Advanced Inland Empire 66ers blanked the High Desert Mavericks, 4-0.
"There is no doubt that, top to bottom, this is by far the most impressive outing we've had from a pitcher this year," 66ers pitching coach Daniel Ricabal said. "Pena threw the heck out of the ball tonight and gave them a very hard time."
The 22-year-old right-hander improved to 7-3 and lowered his ERA to 3.97. It marked the 10th time in 18 California League starts that he's has allowed two or fewer earned runs.
Pena walked Daniel Carroll and gave up a single to James Jones in the opening inning but came out unscathed. He put two more runner aboard in the second but struck out three to keep the Mavs scoreless.
From there, the native of the Dominican Republic cruised. He fanned a pair in the third, then struck out the side in the fourth. He set down two more batters swinging in the fifth and struck out the final three men he faced.
Pena exited after throwing 104 pitches.
"He pitched ahead in the count and did all those good things he needed to do," Ricabal said. "He threw his fastball from 91 to 97 [mph] and punched a bunch of guys out with his slider. It was basically a two-pitch approach.
"Once he got out of the sixth inning at 104 pitches, we knew that was it for the night. He had more in the tank, for sure, but we are thinking about the bigger picture. He has a bunch of big outings in the future and tonight was a stepping stone."
Pena totaled three walks, pushing his league-leading total to 52. He's also third with 108 strikeouts over 99 2/3 innings.
"He's a ways away from the Majors and his command is an ongoing battle," Ricabel noted. "He's a young kid with a power arm, so he will have command problems. But if you look at his last two or three outings, you'll see that he's making it a priority.
"He's working on repeating his delivery and his arm slot and his release point. He's definitely making the progress the organization would like to see."
Pena's previous career high was 12 strikeouts in a complete-game victory for Class A Cedar Rapids last Aug. 21. In 2008, he reached double digits in three consecutive starts in the Rookie-level Dominican Summer League.
Ty Kelley relieved Pena and allowed two hits in the seventh before Caleb Graham struck out four over the final two innings for Inland Empire.