|Chester May meeting|
|Dates: 4-6 May Venue: Chester racecourse BBC coverage: Friday commentary is live on BBC Radio 5 live sports extra from 14:00 BST|
Odds-on favourite US Army Ranger just denied his Aidan O'Brien-trained stablemate Port Douglas to win the Chester Vase.
The 4-11 chance, under Ryan Moore, prevailed by a short head but was eased from 4-1 to 5-1 by bookmakers behind Midterm (7-2) for the Derby at Epsom.
Port Douglas set the pace before US Army Ranger took up the running.
But the runner-up, ridden by Seamie Heffernan, was only just touched off at the finish.
Stewards spoke to Heffernan about the running and riding of Port Douglas but took no further action.
Some observers felt the jockey was following team tactics and could have been more vigorous with his mount in the closing stages, although the horse did twice edge left when he used his whip.
It was only the second run of US Army Ranger's career and Moore said: "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."
O'Brien's 2013 Derby winner Ruler Of The World also warmed up for Epsom with a Chester Vase win, but US Army Ranger was displaced as favourite for the Classic on 4 June by Midterm, winner at Sandown last month.
Analysis - BBC correspondent Cornelius Lysaght
"These Classic trial races sometimes only add to the confusion, and the fact that it was just by a narrow margin that US Army Ranger beat his stablemate certainly didn't seem to do anything to clarify the pre-Epsom situation.
"Bookies reacted pretty quickly by replacing the winner as Derby favourite, with Midterm, but the line from a positive Ryan Moore seemed to be that it was too early to jump to any conclusions about a horse racing for only the second time.
"Port Douglas galloped right into the reckoning with a very solid performance."