BOSTON – Jarrod Parker did his part to nail down his first major league win.

It was up to his bullpen to finish the job.

That proved adventurous, but the A's preserved a 5-3 victory over the Boston Red Sox on Tuesday night and rewarded their rookie right-hander with a well-deserved win.

"I don't think it'll settle in until (today), or when I'm getting phone calls tonight," Parker said.

Parker pitched 6 2/3 innings of four-hit ball in his third career start. He also benefited from an early lead, as the A's used a four-run fourth inning to go ahead 5-0.

Closer Grant Balfour entered in the ninth with a 5-1 lead. Three hits and a walk later, it was 5-3, and Oakland manager Bob Melvin had to call on Jordan Norberto, who recorded the final two outs with runners at first and second to earn his first career save.

The A's stopped a three-game losing streak, but their closer situation is becoming a growing issue.

Balfour failed to convert a save opportunity for the third time in his past four outings. He has allowed six runs in his past four outings after surrendering just one in his first 10 appearances.

Melvin said after the game that Balfour, who had never been in a full-time closer role before this season, remains his ninth-inning man.

"Those types of things happen," Melvin said. "We'll work through it. Nothing's changed. I just had to go get him tonight."

Rookie setup man Ryan Cook is starting to emerge as an alternative should Balfour continue to falter. Cook pitched a scoreless eighth with two strikeouts and hasn't allowed a run in 10 games this season.

But it was Parker – who came from Arizona with Cook and outfielder Collin Cowgill in the Trevor Cahill trade – whose performance had to be most encouraging to Melvin.

Parker struck out four and walked two, establishing his fastball early and mixing in an effective changeup to keep the Red Sox off balance. He estimated he threw only five breaking balls.

"Something we did that was good was move in and out and change the eye level (of the hitters)," Parker said.

Et cetera – ESPNDeportes reported that Edgar Mercedes, who helped Yoenis Cespedes land his four-year, $36 million deal with the A's, has filed an arbitration claim against Cespedes for breach of contract in the Dominican Republic.

Mercedes claimed Cespedes promised to pay 17 percent of his contract to Mercedes' Born to Play Academy for representation, training and food while Cespedes was living in the Dominican Republic. Mercedes also claimed Cespedes owes another 5 percent to agent Adam Katz.

Cespedes declined to comment.

• Illness again knocked left fielder Coco Crisp out of the lineup. Jonny Gomes played left field.

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