The Epsom Derby picture was no clearer after US Army Ranger scrambled home from his stablemate Port Douglas in what turned into a dramatic running of the MBNA Chester Vase on the Roodee on Thursday.

US Army Ranger got the verdict by a short head, but it was followed by a stewards' inquiry into Seamus Heffernan's riding of the runner-up, with both the jockey and trainer Aidan O'Brien having their explanations noted and ultimately no action being taken.

O'Brien was winning the Vase for the fourth year in a row and the seventh time in all, but with several trials still to be run, which horses will represent him in the premier Classic at Epsom on June 4 has yet to be determined.

US Army Ranger was pushed out to 5-1 from 4s with some bookmakers, with Port Douglas slashed from 66-1 to 16s and Sir Michael Stoute's Midterm promoted to 7-2 favourite, although O'Brien's 1000 Guineas winner Minding is 2-1 'with a run'.

However, O'Brien was happy with the Ryan Moore-ridden US Army Ranger, who was having only his second start.

Port Douglas attempted to make all under Heffernan and when US Army Ranger and Moore swept past the race looked over, but the former rallied to give the 4-11 favourite a mighty scare.

O'Brien said: "It didn't really go to plan. We thought Jamie (Spencer on Dwight D) would go on, but then we knew before the race he wasn't.

"Port Douglas was in cheekpieces for the first time, he ran in blinkers for his last two races last year and I didn't want to put them on round this place being sharp and tight. He was very idle in front and didn't get racing until they were together.

"You have to be happy with that. With any trial you don't know what form is going to come out of them. They've pulled seven lengths clear of the Sandown horses (beaten in Classic Trial) so you'd take that.

"I was very happy with Ryan's horse, as he has obviously progressed well and we always thought the other horse would come into his own when he went further than a mile.

"What I most loved about him was his high cruising speed early and he would have preferred if they had been going a lot faster. That's what you want to see.

"We'll see what's going to happen. He's learnt a lot today and wouldn't have had a hard race. They only raced for four furlongs."

Moore said: "He's still very babyish, he travelled really nicely and I just wanted to teach him. When he got to the front he had a bit of a look, as the other horse came back he was just going to do enough.

"He's a baby, it's only his second run and he made his debut five weeks ago - he'll learn plenty. I was probably a bit too kind to him when he first went there and he's probably switched off on me.

"He didn't know how to fight and he'll learn a lot from that. Aidan's other horse isn't a bad horse, he's a Group Two winner carrying a penalty - they are both decent horses."

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