Imperial Monarch gained compensation following his luckless French Derby run by making every yard of the running and surviving a lengthy stewards' enquiry in taking the Juddmonte Grand Prix de Paris at Longchamp.
Aidan O'Brien's Sandown Classic Trial winner suffered a nightmare passage at Chantilly last month before flashing home down the wide outside of runners to finish a never-nearer eighth.
Jockey Joseph O'Brien appeared determined to avoid a repeat, letting his mount bowl along at the head of affairs following a smart start.
The challengers were queuing up at the top of the home straight, with Andre Fabre's Last Train throwing down the strongest bid inside the final furlong.
But Imperial Monarch answered O'Brien's every call and held on in a thrilling finish. Fabre also saddled the third home, Saint Baudolino.
The unluckiest horse in the race was David Lanigan's Main Sequence. Unbeaten in four starts before chasing home O'Brien's potential Triple Crown aspirant Camelot in the Investec Derby at Epsom, the three-year-old was settled towards the rear in the early stages by Ted Durcan.
He attempted to make ground in the straight, but was hemmed in on the rail before eventually getting into the clear.
Just as he was beginning to make significant inroads on the lead group, he was once again left with nowhere to go inside the final furlong and he passed the post in fourth.