Carlos Beltran stopped so abruptly at first base after a first-inning single Tuesday night that it appeared as if he was not hustling on what could have been a double.

The truth was potentially much more painful for the Yankees. Beltran pulled up because he felt tightness and a knot in his right hamstring. A few minutes later, he was exiting the field and heading for a date with an MRI tube.

Luckily for the Yankees, the MRI was clean and Beltran is listed as day-to-day. Still, the injury overshadowed the Yankees’ latest loss, a 7-1 defeat to Cole Hamels and the Rangers before 32,373 at Yankee Stadium.

The Yankees haven’t exactly been hitting the cover off the ball with Beltran, who at 39 has been their best player. After his first-inning hit, Beltran is batting .297 with 19 home runs and 53 RBIs.

Beltran stopped after rounding first base on what could have been a double as the ball was bobbled in the leftfield corner by Ryan Rua.

“When he stopped, I said, ‘Uh-oh, is he hurt?’ ” manager Joe Girardi said. “That was my first reaction. But I didn’t really see him grab anything.”

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Within minutes, it was clear why Beltran didn’t try for second when Girardi and trainer Steve Donohue emerged from the dugout. After a brief examination, Beltran left the field.

“I felt tightness and I also felt like a knot in my hamstring,” Beltran said. “When I was about to turn and touch first base, I felt something unusual, so that’s why I decided to stop. When the trainer and Joe went to see me at first base, I still felt the knot and the hamstring [tightness]. Neither went away. Right now, I still feel it. Thank God the MRI showed it’s a day-to-day thing, that it’s not major. I’m happy about that.”

Beltran was replaced on the bases and then in rightfield by Rob Refsnyder, who probably will inherit some extra playing time along with Aaron Hicks while Beltran heals.

Alex Rodriguez, who returned to the lineup against the lefthander Hamels after getting benched against two straight righthanders, went 0-for-3 with a sacrifice fly and two strikeouts. He could reclaim the full-time DH job while Beltran is out, but Girardi would not comment on his lineup plans for today or beyond.

The Yankees did little against Hamels, who improved to 9-1 by throwing seven shutout innings.

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Hamels outdueled CC Sabathia (5-5), who rebounded from a poor outing and a sprained ankle to pitch into the eighth.

Sabathia’s final line (seven-plus innings, six runs) was worse than he pitched because of Texas’ five-run eighth, which included a misplay by Sabathia and a bad-hop RBI single past Chase Headley that the third baseman originally thought he may have been able to turn into a triple play.

The Rangers scored three batters into the game when Adrian Beltre hit a two-run homer to right. Hamels took care of the rest. He gave up six hits, walked one and struck out seven in an 86-pitch breeze.

The Yankees, after general manager Brian Cashman said they needed to declare themselves as contenders or pretenders, have lost two in a row to the Rangers to fall to 37-39. Signs of frustration are building in the clubhouse and manager’s office.

“It’s definitely frustrating, obviously,” Sabathia said. “We’re not playing the way we want to, but we have to turn it around. It’s time now. We’ve got to play with a little more sense of urgency and try to get this done.”

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Said Girardi: “We need to win games. We need to win games and this homestand has not went the way we wanted it so far and we need to turn it around.”

In the short term, they’ll have to do it without Beltran.