Groves retained his WBA world Super Middleweight title and is now on his way to the finals and will meet either England's Callum Smith or Jurgen Brahmer of Germany in the final.
Groves defended his title for a second time, using his experience to outsmart Eubank and come out ahead 117-112, 116-112 and 115-113 on the scorecards at the Manchester Arena.
Today's bout also represents the semi-final of the World Boxing Super Series, meaning the victor gets a date against either Callum Smith or Jurgen Braehmer come May.
It didn't stop his enthusiasm but Eubank Jr's accuracy continued to suffer, and "The Saint" responding with wide hooks with left and right both hitting the target.
Promoter Kalle Sauerland insisted he would wait for the extent of Groves' problem to be determined before deciding what would happen next, with the beaten Eubank Jr also a possible stand-in.More news: Police searching for missing 4-year-old SC girl
Eubank Jr had hoped this much anticipated domestic contest would elevate him out of his famous father Chris Eubank's shadow but Groves, the naturally bigger fighter, proved to be too shrewd having previously fought the likes of Carl Froch and Badou Jack.
Groves, who has fought in more big fights, used distance wisely to pick and choose his moments. Before you sign up, though, know that you'll only be able to get it on Sky and Virgin boxes in the United Kingdom, according to the ITV Box Office website.
"The way he boxed and tied him up just with the right hand and stole time was, for me, an heroic ending to the fight". I want this more than anything I've ever wanted in my life.
Eubank touched down at one point, but it was not ruled a knockdown. He wasn't dabbing at it so I don't think it was obscuring his vision. He cut me. I couldn't see out my right eye.
Eubank Jr's cut was again opened up and the front and back of referee Michael Alexander's shirt was left caked in blood, with the IBO champion beginning to tire as Groves hovered over him looking to finish him off. Jesus, I wish more MMA was presented like this.