Roaring Lion stamped his class when running out a brilliant winner of the Betfred Dante Stakes at York.
Fifth in the 2000 Guineas at Newmarket less than a fortnight ago, John Gosden's colt was the 3-1 favourite as he stepped up to a mile and a quarter for the first time in this recognised trial for next month's Investec Derby at Epsom.
Mildenberger cut out much of the running, closely pursued by the winner's stablemate, Crossed Baton, while Oisin Murphy kept his powder dry aboard Roaring Lion in the middle of the pack.
Once given his head racing inside the final two furlongs, the American-bred colt readily accelerated to the lead and fairly shot clear, leaving his rivals trailing in his wake as he passed the post four and a half lengths to the good.
Mark Johnston's Mildenberger (7-2) boxed on for second, with Aidan O'Brien-trained 50-1 shot Zabriskie coming from the rear of the field to grab third.
Roaring Lion was cut to around 6-1 for Epsom, making him the clear second-favourite behind his 2000 Guineas conqueror Saxon Warrior, who is as short as 4-6.
Gosden said: "I've always said this is his trip and he's proved himself over a mile and a quarter. I liked the way he hit the line strong. He's galloped out well.
"I think it only pays an enormous compliment to Saxon Warrior, who beat us a neck in the Racing Post Trophy at Doncaster and was imperious in the Guineas.
"I think it just confirms the fact that the best Derby trial is the Guineas and this is probably the second best Derby trial.
"He's never been difficult at home. He's a lovely horse, but he's a playboy. He's inclined not to concentrate sometimes.
"I liked the way he came between horses and went away and won and he didn't do any of his silly hanging left and playing around. He's always been a right old Jack the Lad at home, but he's just professionally got in the zone recently.
"Between ourselves I was expecting a performance like that. I would have been disappointed if he didn't give it."
Asked about the Derby, Gosden said: "I think we'll see how he is over the next few days and if he's in great nick we'll make a decision about which race to go for (Epsom or French Derby).
"We'll discuss it with the owner and the manager and the jockey - the point is if we are in that position it's a wonderful decision to have to make."
He went on: "They (Saxon Warrior and Roaring Lion) are the two nicest colts in Europe, the French Guineas was a bit of a muddle.
"We thought we had him beat and Donny and then I don't know what happened, we all went left, our boy messed about and he came back and beat us fair and square.
"I like Epsom and the Derby, obviously I do, but I'm not putting words in people's mouths. I wasn't surprised by his performance.
"We've given ourselves something to think about. I would have been disappointed if he hadn't done that, to be honest.
"I never shout before a race, but he's been training beautifully since the Guineas.
"He's mentally in the zone now, he hit the line strong so we'll have to work out whether it's Epsom or the Jockey Club.
"His temperament is getting better, he's a complete playboy - his trick is rearing up, but he hasn't reared up for two weeks now he's fit and in the zone, so I think he'll be fine at Epsom."
Murphy said: "He relaxed very good and picked up like a smashing horse.
"His form was very strong, he's very exciting and hopefully he can build on this."
Johnston said of Mildenberger: "My first impression was it was a fantastic run behind an impressive winner. I said to James (Doyle) when he came in 'well done, you made a truly-run trial'.
"But then Charlie (Johnston, assistant trainer) has quite rightly said he maybe didn't go fast enough for his own good, he set it up for a faster horse.
"There's absolutely no doubt he wants further, how much further only time will tell. We've got to be happy.
"We've got a dilemma, we've him and Dee Ex Bee for the same owner, there's the Derby, the King Edward VII and the Queen's Vase to think about.
"Long term the Leger is in our sights, they are two of the nicest types I've had since Bandari."