ESPN

KANSAS CITY, Mo. -- Mariano Rivera tore a ligament in his right knee while shagging balls during batting practice Thursday night, casting a pall over the New York Yankees even before their 4-3 loss to the Kansas City Royals.

The 42-year-old right-hander's leg caught on the field where the grass meets the dirt, causing his knee to buckle. Rivera fell into the outfield wall and down on the ground, where he grimaced in pain while teammates and training staff ran out to see him.

Rivera was carted from the field and taken for an MRI exam, and Royals head physician Dr. Vincent Key diagnosed a torn ACL after looking at scans of the knee.

"I thought it wasn't that bad, but it's torn," Rivera said after the game, pausing several times in the Yankees clubhouse to compose himself. "Have to fix it."

Rivera said that he never gave a thought to getting hurt while chasing balls during batting practice. It's something that he's done his entire career to keep in shape.

He also refused to say whether his career is over. The five-time World Series champion has said he'll make that decision after the season.

"At this point, I don't know," Rivera said. "At this point, I don't know. Going to have to face this first. It all depends on how the rehab is going to happen, and from there, we'll see."

Manager Joe Girardi also dismissed any notion that the 12-time All-Star could have prevented the injury, reasoning that Rivera's pregame routine helped to make him one of the game's stars.

"You've all seen Mo run around here for what, 40 years?" Girardi said. "You can fall off the curb or down stairs and get hurt."

Third baseman Alex Rodriguez was watching from behind home plate when Rivera went down, and immediately said, "Oh, my God." Rodriguez said later that the injury changed the entire tone of the clubhouse, and it didn't improve once the game got going.

Danny Duffy (2-2) went six strong innings before turning it over to the Kansas City bullpen, which maintained a one-run lead until Jonathan Broxton came on to close the ninth.

He allowed a leadoff single to Derek Jeter, his fourth hit of the night, and walked Curtis Granderson. Mark Teixeira followed with a liner to second base, but Chris Getz snagged it in the dirt and fired to Alcides Escobar to start a double play.

Jeter advanced to third for Rodriguez, who hit a chopper to Mike Moustakas at third base. He made a bare-handed grab and threw out A-Rod by a step to preserve the victory.

Broxton earned his fifth save and Kansas City snapped a 10-game home losing streak.

Moustakas homered in the second off David Phelps (0-1), who was making his first major league start, and added a two-run single in the fifth to create some much-needed breathing room.

None of that mattered much to the Yankees afterward.

"That's horrible news," Broxton said. "As many saves as he's been out there and as good an athlete as he is, I just hate for bad news. All I can do is wish him the best."

Bullpen coach Mike Harkey was near Rivera when he went down, and was the first to whistle for help. Girardi was watching batting practice from behind home plate and started running down the third base line, cutting across the outfield to get to his closer.

Harkey and Girardi helped to carry Rivera to the cart, gently setting him into the back with his knee propped up. The cart rounded the warning track before disappearing up a tunnel.

Rivera was examined by Royals associate physician Dr. Joe Noland and team trainers before he was taken to KU MedWest for an MRI exam, which took place during the game. The initial diagnosis was a twisted right knee, and for a while Girardi was optimistic.

That all changed once the MRI exam was taken.

"This is bad. There's no question about it," Girardi said. "This is not what you want to come to Kansas City to hear."

The Royals became the third team in major league history to lose their first 10 home games when they dropped every one during their first homestand. They started to turn things around on a rain-shortened 4-3 road trip, and kept the momentum going against the struggling Yankees.

Mark Teixeira drove in a pair of runs for New York, which has dropped three straight and failed to score more than three runs for the fourth straight game.

Kansas City came out swinging from the start against Phelps, who had appeared six times out of the bullpen before getting the starting nod for the first time.

The Royals left a runner stranded on third in the first inning before Moustakas went deep with one out in the second.

The Yankees couldn't come all the way back against the Kansas City bullpen, whose bend-but-don't-break work over the final 3 2/3 innings left Duffy a winner.

Game notes

Jeter is batting .404 this season. ... The Royals placed Yuniesky Betancourt (right ankle sprain) on the DL purchased the contract of INF Irving Falu from Triple-A Omaha. ... Yankees 3B Eric Chavez was released from the hospital after having concussion-like symptoms Wednesday night. He was put on the seven-day concussion DL and Nix signed to a major league contract. ... LHP CC Sabathia will pitch Friday night for New York. LHP Bruce Chen goes for Kansas City.