NANTERRE, France — Canadian phenom Summer McIntosh claimed the first gold medal of her just-burgeoning career Monday night with a dominating victory in the 400-meter individual medley at the Paris Olympics.

The 17-year-old McIntosh collected her first career medal on the opening night of swimming, taking a silver in the 400 freestyle behind Ariarne Titmus — and ahead of Katie Ledecky.

Now, McIntosh has the best color of all.

She pushed the pace hard through the first half of the grueling race — the butterfly and backstroke legs — to leave everyone in her wake except American Katie Grimes.

McIntosh was under her own world-record pace, but couldn’t keep it going. She touched in 4 minutes, 27.71 seconds, more than three seconds off the mark of 4:24.38 she set at the Canadian trials in May.

But it was more than good enough to vanquish the field in the Olympic final.

Grimes, who is also swimming the open water event in Paris, held on to claim the silver in 4:33.40. The Americans also grabbed the bronze when Emma Weyant touched in 4:34.93.