Brian Johnson gave up six hits Saturday night, tying his career high with the Sea Dogs. One of the hits was a home run.

That’s all the criticism that can be mustered when it comes to Johnson, who continues to cruise through Double-A with remarkable ease.

Johnson threw a seven-inning complete game to lead the Portland Sea Dogs to a 5-1 win over the Altoona Curve in the first game of a doubleheader at Hadlock Field.

Portland made it a sweep with a 3-2 win in the second game.

Blake Swihart knocked in two runs in each game, including his ninth home run of the season.

Johnson improved to 6-1 with a 1.66 ERA in nine starts. He walked none, striking out four. He worked quickly and efficiently, throwing 72 of 105 pitches for strikes.

“I did well locating the fastball in and out,” Johnson said.

Johnson’s forte is that fastball, sitting around 92 mph, which he located well (46 of 55 for strikes). He added a mix of change-ups and curves, with an occasional cut fastball.

Johnson faced 26 batters, and 20 received a first-pitch strike.

“That’s the key, getting ahead of the count,” said Swihart, his catcher. “He was working both sides of the plate and just mixing it up on them.”

Johnson’s one mistake was a hanging off-speed pitch that Willy Garcia crushed over the left-field wall in the second inning.

“I wanted to go change-up down and left it up and in the middle,” Johnson said. “That’s usually what happens with those.”

Johnson gave up a single after the home run, then retired nine straight batters. Since being promoted from Class A Salem after April, Johnson has become a valuable pitching prospect.

But the list of Red Sox pitching prospects is long. Johnson is likely to finish this season with the Sea Dogs. Ask Johnson about his future and he simply shrugs.

“The only thing I’m worried about is getting my lifting in (Sunday) and my bullpen on Monday,” Johnson said.

Since Johnson hasn’t allowed more than two earned runs in a start, he was in good shape when David Chester’s three-run double game Portland a 3-0 first-inning lead. Chester, a first baseman just called up from Salem, has 10 RBI in seven games with the Sea Dogs.

Swihart’s two-run single in the fifth provided insurance.

In the second game, reliever Robby Scott made a spot start for Portland. After giving up a leadoff home run to Drew Maggi, Scott shut out the Curve for four innings.

Michael Olmsted (3-0) pitched two no-hit innings, and Noe Ramirez picked up his seventh save, allowing an unearned run.

NOTES: The announced paid attendance was 7,368. … First baseman Stefan Welch required stitches above his right eye after a collision Friday night with second baseman Sean Coyle. Welch sat out Saturday’s games but said he expects to play Sunday. … The teams will finish their season series at 1 p.m. Sunday. About 400 tickets remain. … In Oakland, Red Sox Manager John Farrell told reporters that “I know Mookie Betts is swinging the bat well … he’s clearly on the radar.”