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6/19/2014 7:19 P.M. ET

McClendon not concerned about Zunino's bat

SAN DIEGO -- After hitting .274 in the season's first month, Mariners catcher Mike Zunino has batted just .188 (24-for-128) in his past 38 games. But manager Lloyd McClendon says the 23-year-old is just going through the normal growing pains and has been a stalwart behind the plate through it all.

"I see a young man that has a bright future, is learning the league and right now he's been swinging and missing a little bit," McClendon said. "But when he shores things up, he's a fast learner. I see a future All-Star catcher, that's what I see. He's in his first full year and he's going to struggle. It happens. They all struggle at some point. He'll be fine."

Zunino is hitting .219 with seven home runs and 22 RBIs in 201 at-bats. He got a normal day off Thursday with backup catcher John Buck starting the day game after a night game against the Padres.

Zunino is tied for second among American League starting catchers with just two passed balls and is tied for the fifth-best caught stealing percentage at 28.9. The Mariners have raved about his ability to block pitches in the dirt and he's been excellent in working with Seattle's pitchers, who have the second-best ERA in the league.

San Diego scored the tying run in Wednesday's 2-1 loss on a wild pitch by Felix Hernandez on a sixth-inning changeup that skittered past Zunino, allowing Alexi Amarista to score from third. But Hernandez acknowledged that was a "horrible" pitch on a ball he spiked in the dirt well in front of the plate.

Zunino's goal is to keep every ball in front of him and he thought he'd done so with Hernandez's tough changeup to Chris Denorfia with two out and the 1-0 lead at the time.

"It just got on the right side of my body," said Zunino. "Obviously, as the ball is traveling, you have to make a read and try to use your body to keep it over the plate. Sometimes it's tough with changeups in general. With breaking balls you know they're going to bounce back the opposite way because of the spin, but with changeups you just sort of have to beat it to the spot. I thought I got there, but it was just a little bit off my right side."

"It's a 90-mph changeup," McClendon said. "It's like a fastball. It's tough. He's been great. It's unfortunate, but he's not going to be 100 percent when it comes to blocking that kind of changeup, and last night was just one that hurt. It happens."

Jones remains in lineup after hit to head

SAN DIEGO -- Mariners center fielder James Jones said his head was fine on Thursday after taking a hard throw off the back of his batting helmet as he sprinted to first base on a close play in Wednesday's 2-1 loss to the Padres.

Jones was knocked off-balance and had to be helped off the field by trainer Rick Griffin after being hit by catcher Rene Rivera's throw on a ball that he'd hit just in front of the plate in the third inning.

"I knew something was wrong, because the first baseman threw his target down and I had a feeling the ball was coming down the line, but I was hoping it would hit me in the back or something," Jones said prior to Thursday's finale with the Padres.

Jones stayed in the game and finished 0-for-4, but said he was just glad he was able to continue playing as the trainers checked him after each inning for concussion symptoms.

"I was afraid because I wasn't answering the questions like they wanted when we were walking off, but I got it back together," Jones said. "They kept following up, asking if I had any stiffness or headaches, but that didn't come up."

Jones was called out on the play when home-plate umpire Tripp Gibson ruled he was out of the baseline when the ball hit him, though that interpretation didn't sit well with manager Lloyd McClendon, who noted Jones was almost right at the bag.

What is a runner supposed to do in that situation, given first base sits on the inside of the line?

"That's what I asked," McClendon said. "I'm baffled by a lot of things. He was right on the line. What's he supposed to do? When you get to the bag, you have to touch the bag. What are you supposed to do, stop and reach out?"

The rookie Jones wasn't going to argue the call, but said replays showed it was extremely close.

"They said I was a few inches off, like I wasn't on the line exactly and I can't interfere with the line right there," Jones said. "One of the coaches saw a video and said my foot was like two inches over or it would have been all right. They said my foot was on the chalk."

Iwakuma on track to make start on Friday

SAN DIEGO -- Hisashi Iwakuma is still dealing with a lingering sore neck, but the All-Star right-hander expects to make his Friday start in Kansas City as scheduled.

"I'm feeling much better," Iwakuma said Thursday through translator Antony Suzuki. "I did my flat ground throwing yesterday and wasn't feeling anything. So that's good progress and hopefully it turns out to be nothing tomorrow."

Iwakuma's neck tightened up during a pregame training room session prior to his last start Sunday against the Rangers and he wasn't sure he was going to be able to pitch when he was having troubles warming up in the bullpen, but wound up throwing eight innings of one-run ball in a 5-1 victory.

Iwakuma skipped his usual bullpen session between starts this week, but did play flat-ground catch both Tuesday and Wednesday.

Manager Lloyd McClendon didn't expect any problems for Friday's matchup against Royals ace James Shields in the first game of a three-game set in Kansas City.

"He's going to make his start," McClendon said. "He's not 100 percent, but he's ready to go unless something drastically changes."

Worth noting

• First baseman Justin Smoak is scheduled to make his second rehab start Thursday night for Triple-A Tacoma as he recovers from a strained quad muscle that has him on the 15-day disabled list until next Wednesday. Smoak will play DH again Thursday after going 0-for-3 with a walk on Wednesday.

"He hit the ball hard a couple times," McClendon said. "We'll keep running him out there and getting him at-bats."

• Right fielder Michael Saunders is expected to begin his rehab stint Friday with Tacoma, while DH Corey Hart is scheduled to return on Saturday. Saunders has been sidelined since June 10 with inflammation in his right shoulder, while Hart strained his left hamstring on May 18.

• After throwing seven innings of one-run ball with three hits on Wednesday, Hernandez ranks first in the American League in innings (113 1/3) and strikeouts (122), second to Anibal Sanchez in WHIP (0.953) and third in ERA (1.22) behind Masahiro Tanaka and Scott Kazmir. He's also tied for third in wins with eight.

Greg Johns is a reporter for MLB.com. Follow him on Twitter @GregJohnsMLB as well as his Mariners Musings blog. This story was not subject to the approval of Major League Baseball or its clubs.