Trey Ball has had better days with his changeup. It didn’t matter.

Ball’s slider was overwhelming.

Ball, a 2013 first-round draft pick, pitched his best game of the season as the Portland Sea Dogs beat the Reading Fightin Phils 7-1 in the first game of a doubleheader Friday night at Hadlock Field.

Portland made it a sweep with a 9-6 win, bolstered by Mike Olt’s grand slam in the third inning.

In the first game, Ball was backed by 12 hits, including a 3-for-4 effort by second baseman Chad De La Guerra.

Boston Red Sox utility player Brock Holt, making his last of three rehab appearances with the Sea Dogs, played shortstop and went 1 for 2 with two walks.

Rafael Devers and Michael Chavis each had two hits in the first game.

Devers, who went 2 for 5 with two walks in the doubleheader, may have made his last appearance at Hadlock Field. Boston’s top prospect leaves Saturday for the Futures Game in Miami on Sunday. He’s also scheduled to play in the Eastern League All-Star Game next Wednesday.

The all-star break is traditionally a time when the Red Sox move some minor leaguers, and Devers could be due for a promotion to Triple-A Pawtucket. He’s hitting .300 with a .944 OPS and 18 home runs.

“All I want to do is keep playing the way I’ve been playing and let the front office people make that decision,” Devers said through an interpreter. “My job is to do my best wherever I’m playing.”

Ball did his best Friday, allowing three hits and no walks while striking out seven in a complete game. He retired the first 13 batters and was eight batters away from a perfect game (minor league doubleheader games are seven innings).

“I don’t think about that,” Ball said. “Just try to go out and repeat what I’ve done all game and make pitches.

“The slider was working really well. My changeup wasn’t on point, but I trusted the slider.”

Repeating his pitches was key for Ball, who has had solid innings this season but few solid games. Ball (3-6, 4.91 ERA) had not gone seven innings this year, and he was averaging nearly three walks per game.

“Outstanding,” Sea Dogs pitching coach Kevin Walker said. “His delivery was on time and consistent. He didn’t rush. He stayed under control.

“There were a couple of at-bats where he went 3-0, and he didn’t let it faze him, stayed under control, got back in the count and won both at-bats. That was a big step forward … His stuff is good. It’s always been about containing that delivery.”

Ball’s fastball topped out at 92 mph and his slider was at 86-87 mph. His bid for a perfect game was broken up by Jiandido Tromp’s double to right in the fifth, and the shutout was done when Chace Numata doubled Tromp home. Ball retired seven of the last eight batters, including a three-pitch seventh inning.

In the second game, Portland (40-43) trailed 3-1 before scoring six runs in the third inning, highlighted by Olt’s slam, his 12th home run of the year.

Reading dropped to 50-35.

NOTES: The announced paid attendance was 4,840. … Josh Smith (4-1) was the winning pitcher in Game 2 with three scoreless innings in relief. … Danny Mars doubled twice in Game 2 and is batting .313.

Kevin Thomas can be reached at 791-6411 or:

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Twitter: ClearTheBases