An animated Monaco was all over Fish’s groundstrokes from the start, breaking in the second game and barely looking back as he wrapped up the win in one hour and 23 minutes.
"I meant every shot that I played, I did. It was a perfect match for me," said Monaco, who has won four ATP Tour events.
"It was unbelievable. That was the way to celebrate my birthday, playing like this. I feel proud and very happy."
The 21st seed will next face defending champion
Monaco arrived in the quarter-finals off the back of confidence boosting wins over Gael Monfils and Andy Roddick, and was clearly ready to add another American scalp to his name when he broke in just the second game of the match.
Enjoying proceedings from the start, the Argentine allowed himself a grin when he completely framed a backhand volley that Fish could not reach before going on to break on consecutive backhand errors from the American.
The break only added to the oddly-flat Fish’s misery; he never looked likely to get back into the opening set, which was only compounded when he drilled a cross-court backhand passing wide to hand Monaco a second break.
Monaco wasted little time in serving out the set, formalising his lead at the first attempt with a first serve percentage of 96 in the opening set.
Things quickly got even worse for Fish when Monaco broke in the opening game of the second set, the Argentine producing a sensational lob that should have landed well wide only to curl back onto the sideline at the very last second.
Not known for being a front-runner, Monaco did have a minor wobble mid-way through the second set when Fish broke back after a lob long and forehand wide from the Argentine.
But he quickly bounced back and re-established his break advantage in the very next game with another stunning lob that the retreating Fish could only just get a racquet frame too, and could not return.
This time there was no mistake from Monaco as he raced through a comfortable service hold to leave Fish serving to extend proceedings.
Clearly not keen on serving for the match lest his nerves got the better of him, Monaco leapt on the Fish serve in the very next game, earning himself three match points when the American sent a backhand into the net.
But only one was needed by Monaco as he produced a barnstorming finish, diving down to his left for a reactionary stop volley that landed just over the other side of the net for the perfect winner.
Fish accepted that he was beaten by a better player on the day.
"He did a lot of things well and I think more than anything else, he shrunk the court extremely well with his movement and that's why I think you saw a ton of errors from me," said Fish.
"I was pressing a lot just because he wasn't giving me anything. He wasn't giving me any errors. He made one error in the first set and served 98 per cent. That's tough to beat."