Aidan O'Brien's colt was a Group One winner at two and finished third in the 2000 Guineas at Newmarket on his only start so far this season.
A muscular issue scuppered Luxembourg's planned Derby run and kept him sidelined for most of the summer.
Nevertheless, confidence was high on his Group Three comeback at the Curragh with the horse sent out as the firm favourite under the stewardship of Ryan Moore.
Taking on five opponents, Luxembourg was niggled along at the top of the straight and while he eventually moved to the front, Insinuendo was poised to challenge after switching to get a run.
The mare appeared to be getting the upper hand inside the 10-furlong distance, but Luxembourg really stuck his head out and was rewarded for his efforts with a neck verdict.
When asked if he was relieved, O'Brien said: "Very, we didn't think he'd ever get here.
"We thought that he had no chance of running after what happened to him. Everyone did a great job to get him over his first mishap, he was off for a long time.
"Then he came back and it wasn't smooth with him. Jamie who looks after him did an incredible job.
"I didn't think he'd get here, our eye was on the Irish Champion Stakes and obviously we knew you couldn't go to a Champion Stakes without a run and this was the only place we could run."