Lewis Ferguson scored a late winner as the 'Dons' knocked Rangers out of the cup, with Steven Gerrard admitting his side were not good enough at Hampden Park.
He remarked: "This one will hurt for a good while. It's Aberdeen's day, we wish them well. They deserved to go through because they created that bit of magic in the business end of the box and they punished us on a set piece, so we got what we deserved.
"I pick the players, I sign the players, I set the game plan so I'll take responsibility for this but what I'll assure everyone is that won't be our last semi-final.
"Without a doubt we will be back in semi-finals and if the players we have now don't improve and start producing the quality in the final third my job is to go and find the players that will do. Otherwise we're never going to win anything."
Umar Sadiq made his first appearance up front for Rangers with Alfredo Morelos and Kyle Lafferty both sidelined, and Gerrard spoke of the striker's performance.
"To be fair to Umar in the last two or three weeks he's shown signs and improvements. Whether that's enough we'll have to judge that moving forward.
"We can't point fingers and blame Umar, the only thing I'd say to him is when you go round the keeper stand up and put it in the back of the net, don't dive or you're going to get a yellow card."