Call it The Warning.

“You’re blowing it now son,” cornerman Angelo Dundee said, “You’re blowing it.”

Sugar Ray Leonard, who was losing to Thomas Hearns after 12 rounds, got the message. Two rounds later he applied the final notes to a boxing masterpiece of ebb and flow, underscored by a sense of anticipation that kept building until it became almost painful. Even when the action slowed, those watching knew they were witnessing something special.

It happened on Wednesday, Sept. 16, 1981 in a stadium built on a parking lot at Caesars Palace in Las Vegas.

Hearns was the unbeaten WBA welterweight champion, who counted 30 knockouts among his 32 victories. Called the Hit Man, he could make various parts of an opponent’s body do different things at the same time, especially when he connected with his right hand. Oddly, Hearns, being from Detroit, was introduced as the Motor City Cobra. Maybe even the sobriquet Hit Man made some people in Las Vegas uncomfortable.

Leonard was the once-beaten WBC champion (having lost to Roberto Duran, a defeat he avenged), but his dazzling hand-speed, Olympic gold medal, winning smile and sense of showmanship made him the glamour fighter and he cast a big shadow over the 6-foot-1 Hearns.

The temperature at fight time was 89 degrees, but it was hotter under the ring lights. The 5-10 Leonard weighed 146 pounds, one pound under the weight limit, while Hearns came in at 145½. This led to much speculation before after the fight that Hearns, whose well-muscled torso was a mismatch for his spindly legs, had unduly weakened himself.

Hearns reportedly was too far over the class limit the night before the fight, and his hotel bathroom was turned into a sauna, causing him to lose too much weight. Manager-trainer Manny Steward said Hearns was weakened, but for different reasons. He recently told me that Hearns had listened to his mother and had a dietitian in camp and that he did roadwork twice a day. “He usually made the weight [limit] at the last minute,” Steward said. “It was the only time we argued . . . before and after the fight.”

At the same time Dundee was telling Leonard he was blowing it, Steward said Hearns dropped his head while seated in his corner. “He was out of fuel,” Steward said. “But I am not taking anything away from Ray Leonard. He closed the show.”

Over the first five rounds, Leonard circled and stayed outside, unleashing an occasional barrage. Hearns stalked, jabbing and countering well.

Suddenly in sixth round Leonard became the Hit Man. A roar exploded from the crowd of some 23,000 fans as Leonard wobbled Hearns with a left hook. Leonard attacked and had Hearns reeling at round’s end.

“Keep that right up,” Steward told Hearns in the corner.

Staying upright was Hearns’ main concern in the seventh round as Leonard had him in trouble for almost the entire three minutes.

In scoring the sixth and seventh rounds I made the same mistake the three official judges made, calling them 10-9 rounds when they should have been 10-8 rounds. If a relatively close round is 10-9, then a round in which one fighter dominates should be 10-8. A fighter often can receive more punishment in a round in which he remains upright than in one in which he is knocked down. In fact, a round in which there is a knockdown can sometimes legitimately be scored 10-9.

The opponent Leonard faced in rounds eight through 11 was Sugar Thomas Hearns, who circled and jabbed. Leonard seemed to be looking for the big punch, and he was landing only single shots. By the end of the 11th round Hearns was back to throwing bombs, and he had the edge in that round and the 12th, both action-packed rounds that had cheers and applause raining down on the ring.

Leonard, bruised about both eyes, heard Dundee’s message, and it was Ray “Hit Man” Leonard who rose from his stool to do battle.

“They even switched boxing personalities,” Steward said in our recent conversation.

A tiring Hearns went back on his bicycle in the 13th round, but Leonard knocked him off it. At one point Hearns went through the ropes, but referee Davey Pearl ruled he was pushed. Near the end of the round, Hearns was knocked into the ropes, and Pearl correctly called it a knockdown because the ropes held Hearns up. The bell saved Hearns, but the end came at 1:45 of the 14th round, with Hearns being battered on the ropes.

Under today’s championship rules, Hearns would have been the winner. After 12 rounds Duane Ford had it 116-112, Lou Tabat had it 117-112 and Chuck Minker had it 117-111, all for Hearns.

Told that he was behind after 13 rounds (Ford 124-122, Tabat 125-122 and Minker 125-121) Leonard said, “I always felt a knockout helped a great deal of the time.”

Especially when you’re blowing it son.