Referee Ian John Lewis jumped in at 1:31 of the round as Munroe was under pressure and backed into a corner. Munroe should have been allowed to continue, as he was throwing back, and much of Selby's attack landed on gloves or arms. Selby at one point had beckoned the referee to come and stop it, but Munroe hadn't been in the fight at all up until that point - the writing was on the wall for the likeable "Boxing Binman".
The difference in size was telling - Munroe (8st 12lb 5oz) struggling to cope with the jab and punch variety from the rangy Selby (8st 13lb 5oz). Munroe's title days had come at super bantamweight before his brief retirement, brought about by comprehensive defeat to Scott Quigg in November 2012. He always turns up in shape however and was making a second attempt at the British featherweight title, having lost over 12 rounds to Andy Morris in 2006.
Selby (18-1) dominated the action from the off, moving from side to side and finding angles to whip in fast shots particularly left hooks to Munroe's body. Rendall was just not getting his punches off at all, and Selby whipped in a right hand at the bell to end the first round which stiffened Munroe's legs. Selby continued to demonstrate his impressive speed and reflexes during the early going, doubling up his left hand and landing to both the body and head of Munroe.
In the fourth Munroe finally began to find the target with his southpaw jab, but only in single shots, still unable to put punches together effectively. Selby was able to drive an unsteady Munroe to the ropes with effective pressure in round five, although Rendall found an escape route and another danger moment passed. Selby can sometimes drift into sparring mode, throwing punches with minimal intent for a man who carries knockout power.
When he asserted himself it was a Selby left hook, right hand which sent Munroe retreating to the ropes again in round six, this time trapped in a corner until the stoppage. Munroe had his senses and made his complaint known to the referee.
The former world title challenger from Leicester drops to 27-4-1 and it is hard to see where he goes from here. He looked slow and unable to let his hands go, losing every round before the stoppage. Selby's promoter Eddie Hearn discussed his man defending the newly acquired European title before looking to secure a world title eliminator for the Welshman later this year.
Anthony Joshua continued his perfect start in the professional ring with a devastating knockout victory over Dorian Darch.
After landing a few fierce punches in the opening round, Joshua ended the bout in the second when he forced his opponent against the ropes and unleashed a series of brutal hits.
And Gary Buckland edged out Gavin Rees in an engrossing all-Welsh lightweight tussle via split decision, elsewhere on the Matchroom card.
Rees, who came up short twice in 2013 in another belter against Anthony Crolla and a one-sided loss to Adrien Broner in Atlantic City which nonetheless endeared him to the American crowd, hinted in the build-up to the fight that he would probably retire if he lost to Buckland.