OAKLAND -- It is a familiar refrain from Joe Girardi, a defensive catcher himself during his playing days, that the Yankees manager would prefer to get stellar defense from his catcher than offense.

Still, the Yankees could use more punch from Russell Martin. The second-year Bombers backstop entered Friday's game batting just .173 with four homers and 10 RBIs in 38 games, but Girardi said that Martin's .321 on-base percentage is encouraging.

"Russell's run into some bad luck," Girardi said. "The one thing Russell has done is he's gotten on base. When you look at his average and then you look at how much he's been on, it's really pretty incredible.

"If he was hitting normal, he'd probably have an on-base percentage over .400, but I've seen some good signs from him. He's hit some balls harder, and we know he's capable of doing more."

Martin had a batting average of just .190 on balls in play (BABIP) entering play on Friday, by far the lowest mark of his career. He had a .252 BABIP last year for New York, hitting .237 with 18 homers and 57 RBIs.

Nova starts for Yankees despite hamstring issue

OAKLAND -- Yankees right-hander Ivan Nova is battling a minor right hamstring issue, though it was not enough to place his start on Friday into jeopardy.

"It was a little tight. He's fine," Yankees manager Joe Girardi said. "There's no issue with that. He said he feels good and there's no issues."

Girardi said that Nova was able to do all of his work normally leading up to his start on Friday against the Athletics, and that the lingering bone bruise on his right foot may have caused a chain reaction of soreness in his leg.

"Sometimes when you have ailments in your lower extremities, you might walk a little different, run a little different," Girardi said. "That causes something to get sore. But he checked out fine."

Bombers bits

• Yankees prospect Manny Banuelos was diagnosed with left elbow soreness, a relief to the organization. Ranked the club's No. 1 prospect by MLB.com this spring, Banuelos is on the Minor League disabled list with Triple-A Scranton/Wilkes-Barre.

• Yankees right-hander David Robertson played catch on Thursday in Tampa, Fla., and felt "pretty decent," according to manager Joe Girardi. Robertson had said that he hoped to join the Yankees in Detroit on June 1, but Girardi indicated that he was not sure that was going to happen. Outfielder Brett Gardner is also expected to try swinging a bat on Monday and is unlikely to be available before the Yankees return to New York.

• On this date in 1947, the Yankees defeated the Red Sox, 17-2, at Yankee Stadium to snap a streak of three consecutive shutout victories.