TRENTON, N.J. — Next time, Drake Britton will be more aggressive.

Britton was outstanding through five innings, allowing a run on three hits before running out of steam in the sixth as the Portland Sea Dogs fell to the Trenton Thunder 7-1 on Monday night at Waterfront Park.

The left-hander mixed a strong fastball with a curveball and slider to baffle Thunder batters through five innings before ending up allowing five runs (three earned) on five hits in 52/3 innings. He struck out six and walked four.

“He was really good,” Portland Manager Kevin Boles said. “He had a real good fastball, used his slider and curve, and had a good feel for the change. He was aggressive with the hitters. I thought he pitched very well tonight, very efficient.”

But Britton would like to have the sixth inning back.

Luke Murton had the biggest blow, a two-out, two-run homer that cleared the 30-foot advertising signs in left-center. Britton walked the next three batters, and the last free pass, to Addison Maruszak, brought Boles to the mound to remove Britton.

“I tried to stay focused on getting out of that inning, but just couldn’t do it,” said Britton, who threw 58 of his 93 pitches for strikes. “I want to focus (next time) on getting more out front and drive it through the zone instead of placing it.”

Still, Britton has pitched much better this season after a forgettable 2011 campaign, when he went 1-13 with a 6.91 ERA for Class A Salem. In five starts with Portland, Britton is 1-2 with a 4.32 ERA.

“He’s tough, the mound presence, the quality game makeup he has,” Boles said. “He’s a competitor and he’s on a mission. The stuff that happened in the past, that’s old history. He’s turned the page and put together quite a few quality performances for us.”

Bryce Brentz provided all the Portland offense with a two-out home run to deep right in the ninth.

“It was a fastball away and I put a good swing on it,” Brentz said.

Portland dropped 3 of 4 in the series while falling to 3-11 versus Trenton. The Sea Dogs host the Thunder for a five-game series beginning Saturday before returning to Trenton for the final time for a three-game series July 7-9.

The Sea Dogs were shut down by Trenton’s Vidal Nuno, a 48th-round draft pick in 2009 who started last season in the independent Frontier League. The left-hander might wind up in the Bronx pitching for the Yankees if he continues his current pace, as he tossed seven scoreless innings of two-hit ball to lower his ERA to 0.89 in seven Double-A starts.

“He threw a great game, kept us off balance,” Brentz said. “He located every pitch, kept his change-up down. It was his night, threw a great game.”

Britton allowed one hit through four innings, but Trenton took the lead in the fifth on Maruszak’s RBI double.