Aidan O'Brien charge, who went off at 15/8 under his son Joseph, won the Group 1 renewal by one and three quarter lengths from 5/1 shot Van Der Neer with pace setter Steeler slipping to third.
In the past 11 runnings of Britain's final Group 1 race of the year, four winners have gone on to win the following summer's Derby at Epsom - most recently Camelot in June - and Kingsbarns was quoted at 4/1 for 2013's race following the victory.
O'Brien's move in paying a £17,500 supplementary entry in place of ante-post favourite Battle Of Marengo paid off as he won the Racing Post Trophy for the seventh time.
Kingsbarns, a son of Galileo trained by O'Brien for the Coolmore Stud trio of John Magnier, Michael Tabor and Derrick Smith, won by seven lengths on his debut at Navan and made an impressive step-up from maiden company.
The two-year-old hit the front with two furlongs remaining and surged away for a cosy victory to firmly establish himself as the latest exciting prospect to emerge from O'Brien's Ballydoyle stables.
Aidan O'Brien said: "We're obviously thrilled.
"When he won his maiden a little under three weeks ago, he'd just arrived and won very nicely. After that we were half-thinking of leaving him alone.
"He's a lovely horse and had done great through the year. We did one little bit of work with him and it was lovely. Then the final exam for the Racing Post Trophy was there.
"He came through it with flying colours."
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- Van Der Neer