When the Boston Red Sox went on their July 31 trading spree, they acquired mostly major league players.

But the one minor leaguer may eventually yield very positive results.

Left-hander Eduardo Rodriguez, 21, is putting up crazy numbers for the Portland Sea Dogs since the Red Sox acquired him from the Baltimore Orioles for reliever Andrew Miller.

Rodriguez made his fifth start for Portland on Tuesday night, holding the Reading Fightin Phils to one run over seven innings – a run scored on a wild pitch with two outs in the seventh.

His five-game total: 311/3 innings, three earned runs, 0.86 ERA.

“My impressions are probably right in line with others: He’s been really impressive,” Sea Dogs pitching coach Bob Kipper said. “He’s wiry with a real loose, quick arm.

“He generates electric stuff. He really does.”

Rodriguez has 35 strikeouts with Portland. Counting his time with the Orioles’ Double-A affiliate in Bowie, he has struck out 104 in 114 innings.

Rodriguez can dominate with a fastball that routinely hits 94 mph, along with a two-seam sinking fastball, change-up and slider.

In Bowie, Rodriguez posted a 3-7 record and 4.79 ERA. That may be why the Orioles were willing to deal him. He attended the last two major league spring training camps for Baltimore but the results weren’t coming quickly enough.

Plus, Rodriguez is eligible for the Rule V draft this offseason so he will have to be placed on the 40-man roster.

Still, Rodriguez is only 21, and the Baseball America publication ranked him the Orioles’ third-best prospect and 65th among all minor leaguers.

Baltimore, of course, did well in the trade, at least short-term. Miller, who will be a free agent after the season, has a 1.08 ERA for the Orioles, and a 0.72 WHIP (walks/hits per inning).

Boston has to like the trade as well, especially with Rodriguez showing instant improvement since switching uniforms.

“My fastball is working much better right now,” said Rodriguez, who has been working both sides of the plate effectively.

There are times that Rodriguez sticks with the fastball, only occasionally mixing in off-speed.

That’s fine with the Red Sox, who always preach fastball command first.

“He loves his fastball and he should. It’s been driving his success,” Kipper said.

“But I’ve seen a lot of good change-ups come out of his hand. It’s a real legitimate weapon. We’re working on the slider to get more depth and he’s come along nicely with it.”

One more thing Kipper likes:

“Seems to be very poised,” Kipper said.

Rodriguez can pitch out of trouble. Tuesday’s outing was not his smoothest, giving up seven hits. He allowed runners on third base three times.

With runners on second and third with two outs in the second, Rodriguez struck out Zach Collier on a change-up.

In the sixth with runners on second and third and one out, Rodriguez faced former major leaguer Jake Fox. Rodriguez jammed him on a full-count fastball. Fox hit a broken-bat line drive right to Rodriguez, who threw to third base for the double play.

It looked like Rodriguez would escape a first-and-third situation with two outs in the seventh. Rodriguez got ahead 0-2 but then slipped – literally.

“I tried to throw the perfect change-up and I slipped in the mud,” Rodriguez said.

Rodriguez bounced the pitch. It reached the backstop as the runner on third raced home.

“Then I get the strikeout,” Rodriguez said, still shaking his head about the wild pitch.

Rodriguez will play a key role in the Eastern League playoffs next week. Then comes spring training next year and a chance to show Boston what he’s got.

“I was surprised by the trade,” he said. “It’s OK. Different team. Different staff. But the same goal: make it to the big leagues.”