The Cubs couldn’t survive one day without late-inning drama after putting their closer on the injured list Monday because of a sore right knee.

In fact, it only got worse when the pitcher who finally put an end to the Athletics’ eighth-inning rally Monday night walked off the mound in pain -- before two more pitchers were needed to finish off the Cubs’ 6-5 victory in the series opener.

Brandon Kintzler, a former All-Star closer and the bullpen’s steadiest performer from the start this season, felt “discomfort” in the pectoral area near the front of his right shoulder, the team said after the game.

He was to be examined again Tuesday morning before a determination was to be made regarding a possible IL stint.

For the right-hander nicknamed “Salt,” his injury could be more significant than Craig Kimbrel’s knee inflammation if it turns out to be much more than a cramp. Kintzler has a 2.33 ERA this season and figured to play a key role in helping the Cubs cover the end of games until Kimbrel’s anticipated return sometime next week.

In fact, manager Joe Maddon said he planned to send Kintzler back out for the ninth inning Monday before he got hurt.

Talk about Salt in a team’s wounds.

“We pride ourselves on next guy up,” said starter Kyle Hendricks, whose only hit allowed in 6 1/3 innings was a two-run homer in the third by Marcus Semien (who added a solo shot in the eighth). “We know we have guys that can pick up the slack.”

The Cubs’ oft-maligned bullpen is expected to get setup man Pedro Strop (neck) back from the IL in the next week or so, which should help offset the loss of Kintzler if he needs an IL move.

On this night, left-hander Kyle Ryan started the ninth instead and after retiring the first two batters, gave up a walk and a hit to bring Semien to the plate with the potential tying run at second.

Maddon then went to newcomer David Phelps, who eventually got Semien on a high, deep fly to left for the final out.

A seven-homer night at Wrigley including four by the Cubs, including two by Javy Baez – a solo shot in the sixth and two-run shot in the Cubs’ four-run seventh.

“It’s hard, but we’ve still got to fight through it,” said Baez of a series of recent injuries, including All-Star catcher Willson Contreras’ hamstring.

Newly acquired outfielder Nick Castellanos added his first homer since last week’s trade from the Tigers in the first and doubled home a run in the seventh during a three-hit game.

Asked about the quick adjustment to a new league, he said: “It’s the same. Big in the box, kick high, swing hard, run fast. That’s about it.”

For all their physical woes these days – not to mention the second-worst road record in the National League – the Cubs continued to roll at home, improving to 4-0 during this homestand to improve the second-best home record in the league to 40-18.

Along the way, they added another game to their NL Central lead – matching their season-high of 2½ games, with the Cardinals’ loss.

“I think we’re in a good spot,” said Baez, who last year suggested the Cubs faltered down the stretch because they had their minds on other teams too much.

“We’re actually not paying attention to other teams,” he said. “It looks like they’re paying attention to us. We’ve had ups and downs, and we’ve just got to try to get that out of the way.”