Scoring a lighting quick and delayed knockdown to the solar-plexus in the first, the writing was on the wall for Conlan almost immediately.
A clash of heads opened up a cut on Conlan in the second, which seemed to spur Ancajas on to retain his title in quick fashion.
Several more crunching body shots later, and two highly-debatable low blows called by referee Steve Gray, and Conlan was taken out of the fight in the sixth.
Conlan can certainly come again on heart alone, although Ancajas looks like the mini-second coming of Filipino compatriot Manny Pacquiao after what was a solid performance on the night.
Earlier, ex-amateur star Paddy Barnes impressed with a powerful display against a fighter out-sizing him considerably.
‘The Leprechaun’ displayed solid combinations against an opponent all too willing to trade in Eliecer Quezada at that was ultimately his downfall.
Dropping Quezada early on and later taking a warning for a low blow, Barnes remained unfazed and in the end produced a world-class body shot to end the contest as the bell ended the sixth round.
Guaranteed a top 10 world ranking with the WBO, Barnes is on course for a world title challenge in 2018.
WBO bantamweight champion Zolani Tete took just eleven seconds to dispatch of challenger Siboniso Gonya as one punch ended the fight early on.
Tete walked towards Gonya and proceeded to unleash a massive right hand to lay the challenger out on his back and relieve the referee of any attempt to count.
The two-weight world title holder instantly turned his attention to a unification with Ryan Burnett, who currently holds two other versions of the world crown.
Jono Carroll managed to become the first to stop Humberto de Santiago as the Irishman scored a third round triumph to continue his pursuit of titles in 2018.
The 25 year-old made it 15 wins on the spin since turning pro and picked up a fringe version of the super-featherweight strap into the bargain.