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7/8/2014 2:00 A.M. ET

Buck DFA'd; Mariners likely to call up Sucre

SEATTLE -- Backup catcher John Buck was designated for assignment by the Mariners on Monday after Seattle opened its seven-game homestand with a 2-0 win over the Twins.

The club will announce a corresponding roster move Tuesday, most likely to call up catcher Jesus Sucre from Triple-A Tacoma.

"Listen, these things are never fun. John Buck is a fine, fine baseball player. I think he has been great for this club, a wonderful individual," Mariners manager Lloyd McClendon said. "We got a catcher at Triple-A that's turning the corner and doing a pretty darn good job. … We just felt it was time."

Buck, an 11-year Major League veteran, turned 34 on Monday. In January, he signed a one-year, $1 million contract with Seattle to help mentor starting catcher Mike Zunino and provide the lineup some right-handed power. In 27 games, Buck batted .226 with one home run, six RBIs and a .579 OPS.

His departure clears the way for Sucre, who at 26 years old, is regarded as one of the best defensive catchers in the organization. The 6-foot, 225-pound Venezuela native has thrown out 50 percent (20-for-40) of attempted basestealers with the Rainiers this season. He's batting .274 with two homers and 16 RBIs.

Sucre made his Major League debut in 2013, appearing in eight games with the Mariners and going 5-for-26 with three RBIs before an injury to his left hand landed him on the disabled list in early June.

"We think that this move makes us a better club," McClendon said.

Maurer impressing, carving out steady role in 'pen

SEATTLE -- When the Mariners recalled pitcher Brandon Maurer from Triple-A Tacoma on June 25, he was a long shot to keep a permanent spot on the big league roster. Top pitching prospect Taijuan Walker was about a week away from making his 2014 big league debut and the Mariners needed to make a corresponding 25-man roster move.

In four subsequent appearances out of the bullpen, Maurer has thrown seven scoreless innings and allowed just three hits. He has fanned nine and held opponents to a .125 batting average.

When the Mariners optioned rookie outfielder Stefen Romero to Tacoma on June 29, it ensured Maurer wouldn't be sent back to Triple-A. Not with the way he's pitching.

"There's nothing like confidence and he's feeling good about where he is at this point," manager Lloyd McClendon said. "That's the reason he's still here. He is a valuable asset to us and he really protects our arms down in that bullpen and he did it again [Sunday]."

Maurer, 24, is in his second stint with the Mariners this season after he went 1-4 with a 7.52 ERA in seven starts before getting demoted to the Minor Leagues. Since returning to the Majors as a reliever, he has added a couple miles per hour to a fastball that already resided in the mid-90s.

"I think I was holding back, trying to pace myself and it wasn't working," Maurer said of his time in the starting rotation. "Here I come out and I know I got one or two innings."

McClendon has been impressed with Maurer's control. The right-hander from California has thrown 66 of 93 pitches for strikes and walked just two since being recalled.

Maurer simply wants to show that he belongs in a bullpen that entered Monday with a 2.47 ERA, lowest in the American League.

"I got to follow suit I guess," he said. "I can't be letting them down."

McClendon undecided on Thursday starter

SEATTLE -- The Mariners haven't announced a starter for Thursday's series finale against the Twins after pushing ace Felix Hernandez's scheduled start back a day to Friday, when Seattle begins a three-game set vs. the Athletics. Oakland is scheduled to open the series with ace right-hander Jeff Samardzija.

But who starts for the Mariners on Thursday night?

"I told you we have options," Mariners manager Lloyd McClendon said. "We just haven't decided what we're doing yet. It's TBA."

The Mariners probably won't promote right-hander Erasmo Ramirez from Triple-A Tacoma. He pitched for the Rainiers on Sunday and would be working off three days' rest. Ramirez has made 11 starts for Seattle this season, going 1-4 with a 4.58 ERA.

McClendon could opt to start a reliever, as the Mariners currently have an eight-man bullpen. Tom Wilhelmsen and Brandon Maurer are capable of throwing up to three innings.

The A's series will take Seattle up to the All-Star break. McClendon said he tentatively plans to go with rookie right-hander Taijuan Walker on Saturday and pitcher Hisashi Iwakuma on Sunday.

"I haven't finalized that yet. As we speak right now, it's Felix, Walker, Kuma," he said. "That could change. I'm just not sure."

Worth noting

• The Mariners have 21 comeback wins this season, fourth most in the American League.

• The Mariners are 28-4 this season when they record 10 or more hits in a game. That .875 wining percentage in those contests ranks first in the AL.

Adam Lewis is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.