As promised, Isaac Cruz was no replacement player.

The 23-year-old from Mexico, called into battle against Gervonta Davis when the scheduled opponent was suspended, gave the “Tank” an unexpectedly stern challenge at Staples Center Saturday night.

In the end, Davis had done just enough to win a close but unanimous decision over Cruz, and he jumped on a nearby turnbuckle in obvious relief when the scores were announced.

There were no knockdowns in the fight, and Davis came the closest to being in trouble against Cruz’s determined attack.

Later, Davis admitted that he hurt his left hand at some point in the fight, which became obvious in the later rounds.

“I was hitting him on the head a lot and i guess it happened then,” Davis said. “As I was going on and on with the fight, I thought I’d bring him down, but then I hurt my hand and I couldn’t do what I wanted to. I’m not a fighter that goes in there and goes for the knockout punch anyway. I just tried to wear him down.”

Asked if this could become the stuff of a rematch, he said, “Hell, no,” which caused some boos from Cruz’s partisans.

Two judges gave Davis the edge, 115-113, and the other favored him by 115-112.

As for Cruz, he proclaimed, “I think you saw a star born tonight,” and he left no doubt that he thought he won.

“That’s my style,” Cruz said. “I’m always pressuring.” But he also said he noticed Davis was having problems with his hand in the first round.

The loss dropped Cruz’s record to 22-2-1 but assured that he’ll be seen in more prominent cards from now on..

Cruz was summoned when  several women came forward and claimed Rolly Romero, the original opponent,  had sexually assaulted them. The WBC suspended Romero and turned to Cruz. Davis knew this wasn’t necessarily good news, since Cruz was ranked No. 8 among lightweights by Boxrec.com and was coming off two impressive decisions over Jose Matias Romero and Francisco Vargas.

Davis came in with a 25-0 record and 24 knockouts, and his first fight in Staples Center attracted 15,850 fans — a sellout, since the promoters had closed off the upper level.

The last thing they, or anyone else expected, was a 12-round fight. Davis had knocked down his opponents seven times in their three previous bouts.

But Cruz landed 112 power shots to Davis’ 113, although he connected at a lower rate.

Cruz made it clear from the beginning that he wouldn’t be intimidated by one of the best one-punch artists in the game today. He knocked Davis back with a right hand in the first round, rallied in the fourth round, and then gave as good as he got in the final two rounds.

An interested spectator was George Kambosos, who lifted Teofimo Lopez’s three lightweight belts last week, with the other one belonging to Devin Haney.

Kambosos saw Haney defeat Joseph Diaz Jr. in Las Vegas Saturday and continued his scouting mission here. He has said he’ll fight anyone in this super-heated division, but the first title defense has to be in Australia.

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Kambosos’ victory has definitely resonated. When the Staples Center videoboard showed the various celebrities in attendance, Kambosos got a bigger reception than Kevin Garnett, Dwight Howard, Kenny Smith, Kawhi Leonard, and Paul Pierce, although Magic Johnson, as usual, got the most enthusiasm.

Davis was noncommittal about his plans. He came down from 140 pounds to his usual lightweight limit of 135 to take on Cruz. But there is no shortage of big-money opportunities.

Not that long ago Vasyl Lomachenko was the leader on several pound-for-pound lists. He lost to Lopez last year. Ryan Garcia, who would have fought Diaz if he hadn’t injured his hand, is also around.

It was a spirited show, the last one before Staples surrenders its name, and the most unmistakable guy in the business provided a nice lead-in to the main event.

Sebastian Fundora is 6-foot-5 1/2 and yet comfortably makes the 154-pound limit. He is only 24, and extended his record to 18-0-1 with a unanimous win over Sergio Garcia of Spain, who came into the event with a 33-1 record.

When you’re punching against the Jolly Green Giant, it’s hard to be accurate, and Garcia connected on just four of his 234 jab attempts. Fundora, punching down at the world as usual, was successful on 55 percent of his shots.

So boxing continues to come up with interesting personalities, despite itself. Cruz turned out to be a compounding bit of interest for Davis, who has no interest in rolling over that account.