“Oh, no. It’s Mo.’’

Those words belonged to catcher Chris Stewart but spoke for the entire Yankees’ organization one year ago today when Mariano Rivera crumbled to the warning track in Kansas City’s Kauffman Stadium.

“I was behind the batting cage and saw some commotion in the outfield. I didn’t know what happened,’’ Stewart said. “Then someone said, ‘Mo went down.’ I said, ‘Oh no, it’s Mo.’ Seeing him getting carted off wasn’t good.’’

Rivera’s season ended shagging batting practice fly balls with a torn right ACL. Surgery followed, and baseball’s all-time saves leader missed the final five months of the season.

Rafael Soriano filled in with 42 saves, so Rivera’s injury didn’t kill the season. Now, he is back at 43 and 11-for-11 in save chances in his final season, but a year ago seeing Rivera on that warning track was scary.

David Robertson was standing next to Rivera when Rivera tumbled to the ground while shagging Jayson Nix’s batting practice fly ball. Robertson’s initial reaction was laughter.

“I laughed when he fell down,’’ Robertson said. “I knew he would have been laughing if it was me.’’

Quickly, the laughing stopped.

“He rolled over and I saw the agony on his face. I knew it was bad,’’ Robertson said.

Brett Gardner was in left field, and the first sensation told him it was bad.

“It wasn’t good, there was no way around it. My first thoughts weren’t good,’’ Gardner said. “I was wondering if this was the end for him.’’