Catcher Gustavo Molina, who was designated for assignment by the Red Sox on Sunday, has cleared waivers and will return to Triple A Pawtucket with the PawSox in the midst of a four-game series with the Toledo Mud Hens.

Molina, 28, went 1-for-7 in the four games he appeared in for the Red Sox. He was called up on June 29 due to the injuries of catchers Victor Martinez and Jason Varitek, but with the team carrying three catchers on Sunday (Dusty Brown, Kevin Cash), a backstop was expendable when the team called up pitcher Michael Bowden.

Red Sox starter John Lackey pitched well, but suffered his first loss since May 21. (AP)

Three times this year the Red Sox have taken the first two installments of a three-game set against the Orioles. And three times, the Sox have failed to put the final touch on a broom job against the team with the worst record (25-56) in the majors.

On Sunday, O’s rookie Brian Matusz shut down the Sox offense, delivering six shutout innings to out-pitch Red Sox starter John Lackey and lead Baltimore to a 6-1 victory.

WHAT WENT WRONG FOR THE RED SOX

–Orioles starter Brian Matusz had not been particularly effective against his fellow portsiders entering Sunday’s game, having been tagged to the tune of a .312 average and .834 OPS by lefties, compared to marks of .271 and .743 against right-handers. But a pair of left-handed hitters for the Red Sox had miserable afternoons against the Baltimore southpaw. David Ortiz and J.D. Drew combined to go 0-for-6 with five strikeouts against him, as Matusz featured a slider that bordered on unhittable for lefties on Sunday.

–Gustavo Molina, on the roster due to the injuries not just to Victor Martinez and Jason Varitek but also Triple-A catchers Mark Wagner and Dusty Brown, had a poor day on two fronts. With runners on first and second and no outs in the third inning, he popped up a bunt attempt, a failure that led to the Sox wasting one of their few early offensive opportunities. Then, with a runner on first and none out in the fifth, he struck out with a terrible swing on a slider at his front foot.

Yet Molina’s offensive limitations to the Sox were known. But he was expected to contribute solid defense, with manager Terry Francona noting upon the catcher’s call-up that he has excellent hands. That made his struggles on Sunday surprising. In the fourth inning, with a runner on third, he failed to move his feet on a wild pitch to his right, instead stabbing at the ball with his backhand on a run-scoring wild pitch. Then, with a runner on second and two outs, he committed a passed ball on a fastball slightly up and to his left.

After the passed ball, Lackey pounded his glove and yelled, “Let’s go,” while waiting for the ball back.

–Marco Scutaro thoroughly botched a double-play grounder in the eighth, first kicking the grounder and then — despite having plenty of time to get Orioles second baseman Ty Wigginton — bounced his throw to first for an error. Scutaro also went 0-for-4, ending his nine-game hitting streak.

–Drew, who went 0-for-4 with three strikeouts (his third hat trick of the season, and first since May 30), committed his first error of the 2010 season on a fly ball he lost in the sun.

WHAT WENT RIGHT FOR THE RED SOX

– Though he suffered his first loss since May 21, John Lackey featured some of his best stuff of the season. He matched a season-high with seven strikeouts and held the Orioles in check through seven innings, allowing just two runs before permitting a couple more (aided by Scutaro’s error) in the eighth. On the day, he allowed four runs (three earned) on eight hits and one walk. Still, even with the loss, over his last eight starts, he has a 5-1 record and 3.71 ERA.

He also once again proved a workhorse, throwing 117 pitches. It marked the ninth time this year that he has thrown at least 110 pitches, and sixth time he has thrown 115 or more pitches. The rest of the Red Sox staff has just four games with 115 or more pitches.

–Kevin Youkilis clubbed his 17th homer of the season in the bottom of the ninth inning, helping the Sox to avoid their fourth shutout of the year. Youkilis also crushed a ball to the warning track in right center that was tracked down.

–Though he went just 1-for-3 with a walk, Red Sox second baseman Bill Hall swung the bat extremely well. He sent a rocket off the base of the Green Monster for a single and flied out twice to center, including a well-struck warning track fly ball in the seventh.

–There was the matter of the Sox having six All-Stars named to represent the American League.

Victor Martinez is likely to be placed on the disabled list on Tuesday. (AP)

According to a source familiar with the situation, the Red Sox are likely to place catcher Victor Martinez on the disabled list on Tuesday and to promote catcher Gustavo Molina from Triple-A Pawtucket. Another source said that a final determination will not be made until Tuesday.

Molina, 28, is hitting .239 with a .292 OBP, .418 slugging mark and .710 OPS in 21 games for the PawSox. Molina is in his 11th professional season, and his fifth organization. He has appeared in 19 big-league games, batting .118/.162/.147/.309. He is unrelated to the three Molina siblings who are currently in the majors.

Martinez is hitting .289/.344/.480/.824 with nine homers and 38 RBI for the Sox this year. Since May 19, he is hitting .371/.424/.619/1.043 with four homers and 19 RBI in 30 games. The 31-year-old has played in 66 of the team’s 77 games this year.

The Red Sox officially announced their minor league deals with right-handed reliever Joe Nelson and catcher Gustavo Molina. Both players have been added to the roster of Triple-A Pawtucket. The team also announced some changes to its baseball operations department.

The press release follows. For more information on Nelson, click here.

The Red Sox today announced the signings of catcher Gustavo Molina and right-handed pitcher Joe Nelson to 2010 minor league contracts. In addition, both players have been invited to Boston’s Major League Spring Training camp as non-roster players.

The announcement was made by Executive Vice President/General Manager Theo Epstein.

Molina, 27, spent all of last year with Washington’s Triple-A Syracuse affiliate, batting .209 (44-for-211) with two home runs and 24 RBI in 72 games. He appeared in 68 games behind the plate, posting a .986 (6 E/415 TC) fielding percentage while throwing out 16 of 39 attempted base stealers (41 percent). Originally signed by the Chicago White Sox as an international free agent in 2000, Molina has played 19 Major League games for the White Sox (2007), Baltimore Orioles (2007) and New York Mets (2008), batting .118 (4-for-34) with one RBI.

Nelson, 35, split last season between the Tampa Bay Rays and Triple-A Durham. He began the year with the Rays, going 3-0 with three saves and a 4.02 ERA (18 ER/40.1 IP) in 42 relief outings before an August 1 option to Durham. The right-hander made 13 appearances for the Bulls, going 2-2 with a 6.23 ERA (12 ER/17.1 IP).

He returns for a second stint with Boston after pitching in three games for the club in 2004. Originally selected by Atlanta in the fourth round of the 1996 draft, Nelson is 7-2 with 13 saves and a 4.07 ERA (65 ER/143.2 IP) in 149 career Major League games for the Braves (2001), Red Sox (2004), Kansas City Royals (2006), Florida Marlins (2008) and Rays (2009).

Both players are on the Pawtucket roster.

RED SOX ANNOUNCE CHANGES IN BASEBALL OPERATIONS: The Red Sox today announced three changes in Baseball Operations. Eddie Romero, who has served as Coordinator, Latin American Operations since 2006, was promoted to Assistant Director, Latin American Operations. Gus Quattlebaum was promoted to Assistant Director, Amateur Scouting after working for the club as a Major League scout since 2006. Steve Peck was named a Major League scout. He joined the Red Sox in 2009 as a professional scout after 13 years on the coaching and scouting staff of the Seattle Mariners.