PORTLAND — One reason why the Portland Sea Dogs rebounded from a horrendous April was improved pitching.

Starter Billy Buckner was one of the standouts, leading Portland with four wins and a 3.20 ERA.

So, naturally, Buckner is no longer with the Dogs, having been promoted to Triple-A Pawtucket.

But the rotation opening has been filled with potential.

Lefty Drake Britton makes his Double-A debut tonight as the Sea Dogs return to Hadlock Field for a 7 p.m. game with the Bowie Baysox.

Britton, 23, has worn the prospect label since the Red Sox drafted him in 2007 and swayed him from a Texas A&M scholarship with a $700,000 signing bonus.

His development was slowed by Tommy John surgery in 2008 and the Red Sox have brought him along slowly. In 2010, Britton pitched for low Class A Greenville, earning a 2.97 ERA in 76 innings.

Before the 2011 season, Baseball America ranked Britton as Boston’s No. 3 prospect, citing his mid-90’s sinking fastball and plus slider.

But Britton bombed when he moved up to advanced Class A Salem last year, going 1-13 with a 6.91 ERA.

His promise peaked through in spurts, but the command and consistency disappeared quickly.

In the offseason, the Red Sox needed to make a decision on Britton. He was eligible for the Rule 5 draft, meaning he could be taken by another team if he was not on Boston’s 40-man roster.

Although his numbers were terrible, Britton’s potential was still there, so Boston protected him on the 40-man.

He began the 2012 season in Salem and it did not look good, with a 1-3 record and 10.71 ERA in April.

But Britton turned it around in May: 2-2, 2.10.

“Drake has consistently shown excellent stuff throughout the year,” Red Sox Director of Player Development Ben Crockett said.

“He’s worked really hard with (Salem pitching coach) Kevin Walker on maintaining his aggressive approach in all situations and, with these adjustments, we felt like he was ready to be challenged in Double-A.”

The Sea Dogs also improved in May. After going 7-18 in April, Portland put up a 15-13 mark in May and is 1-2 in June.

Among the other additions to the Sea Dogs roster is Ryan Kalish, who is on a major league rehab appearance. Kalish played for Portland in 2009 and was with the Sea Dogs in 2010 season before reaching the majors that year.

Injuries to his shoulder and neck wiped out the 2011 season, and now Kalish is working on a comeback.

He began his rehab with an assignment in Salem. He has played three games with the Sea Dogs, going 2 for 9 with four walks.

AMONG THE PROMOTIONS this week are Mike Piazza’s trick dogs tonight, a Josh Beckett bobblehead give-away to the first 1,000 fans Wednesday, the Unum Teacher Hall of Fame inductions on Friday, and the Kastaways band playing before Saturday’s game.

Staff Writer Kevin Thomas can be contacted at 791-6411 or at: [email protected]

Twitter: ClearTheBases