Saunders finished and started the fight the significantly better fighter, out-working his opponent who appeared to have now Plan B when the rounds mounted up against him.
Monroe produce a late rally in an effort to counter the weight of the scorecards but it proved to be too little, too late as the judges gave the WBO champion his belt back.
But he could hardly claim to have stamped his name on the ring in Las Vegas and either Saul Alvarez or Gennady Golovkin could both potentially find more entertaining and more deserving opponents.
Saunders had been anything but quiet in the build-up, posting foul-mouthed messages on Twitter aimed at Monroe and gate-crashing the American’s media workout.
The Brit’s young son Stevie joined in on the act at the weigh-in, aiming a punch at the groin of Monroe before security intervened.
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Saunders was unapologetic afterwards, citing self-defence after Monroe patted the boy on the head, and his father came out similarly aggressive in the early rounds.
The Brit was repeatedly the first to the punch and was in the ascendancy, rocking Monroe at the end of the third with two big left hands and a right upper cut.
The American’s corner complained rightly about some strikes to the back of the head but Saunders was not docked a point – although karma appeared to strike when a head-clash cut his right eye.
Trainer Dominic Ingle told him it was “a scratch” and so it proved as he was hindered by the blood from his eye only in the round in which it happened.
Monroe had good patches in the fight but his inactivity and efforts to counter had little impact.
When the American in the eighth round did open up, he found himself caught by a fine counter shot, perhaps showing why he was so reticent to make the first move earlier in the fight.
Monroe probably produced his best round of the fight in the eleventh, flying out of his corner in stark contrast to anything he had shown before.
But the main positive for Saunders came in the later rounds – where he would previously have run out of steam entirely, the newly focused 28-year-old, working in Sheffield with the no-nonsense Ingle, showed more stamina in the 12th even if he could not find any telling shots to put his opponent on the canvas.
He may yet be a couple of fights from a clash with Golovkin or Alvarez but he is growing up – slowly.