Pedro Martinez shook hands with Luis Diaz in the Portland Sea Dogs’ clubhouse and it was hard to tell who looked happier.

As Martinez walked out the door, he was still beaming.

“Outstanding. Outstanding. I’m very proud,” said Martinez, the former Red Sox great who now works with Boston’s minor league pitchers.

Diaz, 22, had just pitched his first game at Hadlock Field and only his second in Double-A, and he showed the poise of a veteran, lasting eight innings, holding the New Hampshire Fisher Cats to one run on seven hits and two walks Monday night. He struck out two.

“He’s a professional,” said catcher Blake Swihart. “Established the strike zone early and getting those hitters chasing.”

Diaz needed only 83 pitches (56 strikes), to improve to 2-0 with a 1.29 ERA.

He wisely has listened to Martinez’s advice.

“He told me to focus and throw my fastball for a first-pitch strike,” Diaz said.

Diaz signed with the Red Sox in 2008 as a 16-year-old out of Venezuela. His breakout season came last year in low Class A Greenville (7-4, 2.05).

“I became consistent,” Diaz said. “You have to throw down in the zone for strikes.”

Diaz was promoted to advanced Class A Salem last August and helped the team on its championship run.

“He was very impressive,” said Sea Dogs Manager Billy McMillon, who managed Salem last year. “He throws a lot of strikes and that’s what you like to see.”

When Diaz arrived in Salem last year, he replaced Mickey Pena, who was promoted to Portland. Last week Diaz replaced Pena again after Pena was suspended for 100 games for a third positive test for drug abuse.

Diaz has allowed a total of eight hits and two runs in two starts. His fastball was consistently hitting 92-93 mph, and his curve and change-up produced swings and misses.

If Diaz keeps improving, Boston has a decision on its hands. Diaz will be eligible for the Rule V draft after the season unless he’s put him on the 40-man roster.

SHORTSTOP DEVEN MARRERO entered this year with a .258 average in 1½ pro seasons. He still was invited to Boston’s major league spring training camp because of his spectacular defense.

And now he’s hitting, too. Marrero was named the Eastern League Player of the Week after batting .650 over six games last week.

Marrero, 23, a first-round draft pick out of Arizona State in 2012, is batting .291 after going 1 for 4 Monday with his fourth home run.

SEAN COYLE spent three weeks in May on the disabled list or likely would be among the Eastern League’s top hitters. Coyle, batting .346, would be ranked third in the league if he qualified. Going into Monday’s game, Coyle was 24 plate appearances short of qualifying.

If he keeps playing – and hitting – he should be among the leaders sometime in July.

A COUPLE of former Sea Dogs switched teams recently. Pitcher Caleb Clay (Portland in 2011 and 2012) left his team in Korea and was signed by the Los Angeles Angels and sent to Triple-A Salt Lake City. He started Sunday, and allowed three hits and one run over 52/3 innings.

Shortstop Argenis Diaz (2008-09) is now with his fifth organization, signing with the Arizona Diamondbacks and sent to Triple-A Reno.

The Red Sox traded Diaz in 2009 to the Pirates for Adam LaRoche. Diaz played 32 games in Pittsburgh the next year but has been in the minors since, with the Pirates, Tigers and until last week, the Reds.

When the Red released Diaz, they also released Shelley Duncan, a former slugger in the New York Yankees’ system. Duncan played for Trenton and won the Eastern League All-Star home run derby when it was held in Portland in 2005.

Kevin Thomas can be reached at 791-6411 or at:

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Twitter: ClearTheBases