As promised, David Haye made hay before the sun shone early Sunday morning in London.

The unified cruiserweight champion promised all week that though it would be a late night for fight fans at the O2 Arena to accommodate American television, it would be a short one for WBO cruiserweight champion Enzo Maccarinelli. And the WBC-WBA-RING magazine champion made good on his word with one thunderous straight right hand.

That Hayemaker ripped into Maccarinelli as he stood straight up while retreating and sent him heading toward the floor with just over a minute to go in round two of a fight that had begun at just after 2 a.m. local time. Had Maccarinelli followed his legs’ suggestion and gone to the ground immediately perhaps he would have survived but he did not and that, along with a following flurry of Haye punches, finished him at 2:04 of the round.

Instinctively, Maccarinelli reached out with his right hand and grabbed the ropes as he felt himself slump toward the floor, breaking a fall that would have at least momentarily put the breaks on Haye’s assault.

Though still upright, Maccarinelli was all but defenseless and Haye jumped all over him with a wild flurry that ended with a second booming straight right hand to the face before referee John Keane could get between them. Maccarinelli slid along the ropes and fell to the floor as the referee began a count the WBO champion seemed unlikely to beat.

Somehow he did but when he arose Maccarinelli’s legs were as firm as over-done macaroni. He tottered blindly to his right several steps as Keane continued his count, then spun and walked back toward the turnbuckle as his eyes looking vacantly in the direction of a wildly hollering crowd of over 20,000 Haye supporters.

Keane took one long, hard look at Maccarinelli as his stablemate and friend, undisputed super middleweight champion Joe Calzaghe, stood below him just outside the ropes and stared silently in his direction. Calzaghe offered no advice for there was nothing to say except, perhaps, “What were you thinking?’’

Maccarinelli had done none of what Calzaghe’s father, the trainer Enzo Calzaghe, had instructed him to do and paid a concussive price for it that was not lost on Keane. After a moment of consideration, Keane wrapped his arms around Maccarinelli and said no more, a decision no one who had the WBO champion’s best interest at heart could dispute.

As Maccarinelli stood alone, stunned at the thought of how quickly he had been dispatched, Haye climbed the ropes and smugly stared out at the crowd, which had come to an arena only a few blocks from the neighborhood in which Haye had grown up in hopes of seeing exactly what he had delivered.

Haye had returned to London from his adopted home in Cyprus to deliver exactly what he had promised – unifying the 200-pound title in what he said would be his last appearance as a cruiserweight before moving up to the heavyweight division in dominating fashion.

“The Hayemaker doesn’t lie!’’ Haye (21-1, 20 KOs) said. “If I say I’m going to do something I do it. I’m a class above! He’s the No. 2 cruiserweight in the world. I’m No. 1 and the difference between 1 and 2 is a big, big difference.’’

Certainly it was from the outset. Although both were cautious, Haye landed a smashing right hand in the first round and a second one midway through the second round. Neither wobbled Maccarinelli but both landed so solidly it was obvious there was a limit to how many of them he could take. As it turned out that limit would be only one more.

When that third straight right exploded onto Maccarinelli’s chin, the WBO champion slumped forward before pitching back and heading down until his right hand interrupted his fall. Soon after, David Haye would finish the job in a way that left no doubt who the best cruiserweight in the world was, even if he would soon be leaving that division in search of bigger game.

“Heavyweight boxing is a disgrace,’’ Haye said. “It’s a sucky division. It’s time for me to clean up the division. They can’t run from The Hayemaker.’’

Neither could Maccarinelli (28-2, 21 KOs), nor did he try. Instead he simply came forward and back in a straight line, offering Haye no angles to contend with. Worse, when he retreated he repeatedly lifted his head up, creating a wide open target for Haye to attack.

“I just didn’t follow the plan,’’ Maccarinelli admitted. “I kept pulling my head straight back. I’m going to get crucified back in the changing room (by the senior Calzaghe).

“I’m kicking myself in the back side for the way I boxed. I was under orders not to pull back with my head up and I did and I got caught.

“Seeing the replay I was in no position to continue. I made a mistake and I got caught. He saw me hurt and finished me off. Simple as that.’’

This fight had been nearly five years in the making and looked for a time like it might never happen after Haye moved up to the heavyweight division and won before slipping back to the 198 pounds he carried into the ring Saturday night to close his time as a cruiserweight by first dethroning WBC-WBA champion Jean Marc Mormeck and then leaving Maccarinelli cold. In the end, he had more trouble carrying all those belts he now owned out of the ring than he ever had garnering them inside it.

Haye went on at some length after his hand had been raised about what he would now do to the much larger men in the heavyweight division. Yet doubts remain for many because Haye has not only been stopped by cruiserweight Carl Thompson but also dropped by Mormeck and others so his chin remains suspect, although his punching power is not.

Enzo Maccarinelli intended to test that chin but he could not stay around long enough to do it. David Haye believes the same will be true for the bigger but slower men he now will be facing.

“I’ve said since I was a little boy I’d be heavyweight champion,’’ Haye said. “There’s nothing these heavyweights can do. The bigger they are the harder they fall. I’m coming for those heavyweights. They better start running.’’

That’s some advice Enzo Maccarinelli would have been wise to follow for a time himself.