READING, Pa. — The Portland Sea Dogs got off to a rough start Thursday, swept by the Reading Phillies in an opening-day doubleheader.

The Sea Dogs lost the opener 4-2 on Leandro Castro’s walk-off homer, then the second game, 7-4.

Bryce Brentz, the top power prospect in the Boston Red Sox organization who was making his Double-A debut, ended the day with three straight hits, including a pair of singles in the late innings that helped give the Sea Dogs a chance to rally in the second game.

Portland trailed 7-1 before Brentz singled and scored in the sixth, then added a bases-loaded single in the seventh to make it 7-3.

Phillies closer Justin Friend entered at that point and slammed the door, inducing a Reynaldo Rodriguez double play that drove in a run but essentially killed the rally.

“It’s always disappointing,” Brentz said of losing on opening day, “but the thing about baseball is there’s always tomorrow. We put ourselves in good situations, we just didn’t get timely hitting – they did – and timely hitting wins ballgames.”

Five double plays hurt the Sea Dogs in the nine-inning opener – doubleheaders are scheduled for seven-inning games – when they had 12 hits.

“Credit to their pitcher, he got the plays when he needed them,” Brentz said of Reading starter Jon Pettibone. “You tip your hat to him and their ballclub for fighting and playing hard. We’ve just got to come out better and get better hits, timely hits.”

“Our guys swung the bats well and sometimes you’re going to hit the ball at people,” said Portland Manager Kevin Boles. “We liked our guys: They had an aggressive approach and we’re really pleased with how they managed the strike zone.”

The Sea Dogs took a 2-1 lead in the seventh inning of the opener on Ryan Dent’s solo homer but couldn’t hold on.

In the bottom half, the Phillies put the first three batters on against Aaron Kurcz, then got a tying sacrifice fly from Jiwan James.

Two innings later, Castro slammed a two-run homer to end it.

“I thought our guys played well,” Boles said. “We swung the bats well. (Starter Chris) Balcolm-Miller (five innings, three hits, one run) was outstanding. (We) played solid defense. There were a lot of positives in Game 1. We were really happy with how the guys played.”

Other than Brentz, who went 3 for 4 to cap a 4-for-7 day, there were few highlights in the second game.

The Phillies scored four times in the third off starter Chris Martin and went up 7-1 in the fifth on Castro’s two-run single.

Brentz at least gave the Sea Dogs a highlight. The Red Sox are expecting big things from a player who hit a combined 30 homers last season at two Class A stops.

“He’s an aggressive hitter,” Boles said. “It looks like he’s got a solid approach and he was able to work to all fields tonight. It was pretty impressive.”

“I’m happy with what happened tonight, not as far as wins go but myself, being the first opening day in Double-A ball,” Brentz said. “I’m pretty pleased.

“This is a separator league. You’re not in A-ball anymore. I know for me there’s some things I need to work on. Everybody’s got to work on things.”

NOTES: J.C. Linares homered and singled in the second game, and went 4 for 7 overall for the Sea Dogs. He was hit in the right hand with a pitch in the second game but singled in his next at-bat The Sea Dogs dropped to 9-10 all-time in openers.