Snellen just held off the late lunge of favourite Pearls And Rubies to provide Champion Hurdle-winning trainer Gavin Cromwell with a second Royal Ascot winner.
Sent off at 12-1 having won on her only previous outing at Limerick, she was produced with a well-timed challenge by Gary Carroll.
With a furlong to run there were any amount still in with a chance, but Carroll’s mount took a length out of the field.
That should have put the race to bed but Snellen began to drift to her left, allowing Pearls And Rubies and Ryan Moore a chance to close the gap. Unfortunately for favourite-backers, though, there was still a head between them when the line came.
Golden Mind and 125-1 shot Oddyssey dead-heated for third.
Cromwell said: “She’s been nice from the word go and is just progressing all the time.
“Her dam won over a mile and a half so I think she’ll stay further. I haven’t thought about Classics, we’ll enjoy today first.
“I’ve been very fortunate to have had two runners at this meeting and both are winners.
“Quick Suzy was a very different type of filly. She won the Queen Mary and was very much a two-year-old.
“This filly has more scope and is much more of a long-term prospect.”
He added: “She’s in the Moyglare and that’s the obvious race for her.
“I didn’t have a Royal Ascot runner until two years ago and said I wouldn’t come to the meeting until I had a runner.”
Carroll – who also rode Quick Suzy – paid tribute to Cromwell.
He said: “Gavin Cromwell is doing some job with these horses, without a doubt. Whether it’s three miles or five furlongs, he gets the best out of everything. But Gavin, all he wants to do is improve, there’s no airs or graces. He said he went down and spent a day with Joseph O’Brien, last year spent a day with Paddy Twomey, even to just try to pick up something. His results are showing.”
Of the Aidan O’Brien-trained runner-up, owner Richard Henry said: “She went to win her race, and maybe got a bit lonely on her own. She has run a great race. She will come on for the run. She is a sweet filly. Ryan thinks she could be very good.”