The 1 1/16-mile event is the second jewel of the Triple Tiara, for three-year-old fillies, foaled in Canada.
The daughter of Tethra overhauled Authenicat in the final 70 yards to capture her first career added-money triumph. Victory Romance finished third.
Owned and bred by Knob Hill Stable, Nicki Knew traveled 1 1/16 miles in 1:44.82.
Partnering the Kevin Attard trainee in her second try around two turns was jockey Jim McAleney, who also won this year's Eclipse Stakes with True Metropolitan.
"I was very happy with the way this filly was going into the race," said McAleney. "Kevin (Attard) had her so happy and in such good order. A happy horse is dangerous. I said to him this morning, 'I wouldn't trade horses with anyone.'"
In the trailing position after three-quarters of a mile, Nicki New began to pass fillies one by one on the second turn. Staying on strongly through the stretch, she rambled up to the flank of Authenicat and drew off late for a 1 1/4-length tally.
McAleney said Nicki Knew overcame a wide trip to prevail over her six rivals.
"We lost a bit of ground. It wasn't an ideal trip. She had to be the best horse today. I had a lot of confidence in her," offered McAleney.
Attard, who won last year's second jewel of the Canadian Triple Crown with Alezzandro, said he always believed the homebred filly was a candidate for distance racing.
"We were looking forward to stretching her out. She had trained well as a juvenile. At that time, we thought she would go long. Today, everything came to fruition," said Attard.
Nicki Knew raised her earnings to $271,180.
The third jewel of the Triple Tiara series is the 1 1/4-mile Wonder Where Stakes, slated for July 26.
Nicki Knew returned $17.30, $9, $4.10, combining with Authenicat ($5.10, $3) for an exactor worth $77.40. Victory Romance ($3) rounded out a $274.10 triactor.