The 54-year-old father of two from Edinburgh mastered the stiff breeze to fire a two-under-par 69, one of only four scores under 70.
"Any time you shoot under par on a golf course as tough as this in a major championship you have to be pleased," said Oldcorn. "I could not be happier.
"You can imagine how difficult this course would be if the weather was bad. It is so difficult to keep the ball on the right part of the fairways. All I tried to do was just aim for the middle of the greens and get as close to the pin as possible.
"There are two or three holes out there which are virtually unplayable, such as the short 15th, where just keeping the ball on the green is a success."
Oldcorn went to the turn in level-par 35 with two birdies offset by two bogeys. On the homeward stretch, he had seven pars and birdie 3s on the 11th and 14th holes, where he knocked in useful putts
He goes into today's second round four strokes adrift of leader Bernhard Langer, who was beaten in a play-off for the title at Royal Birkdale last year. The German played some brilliant golf for his 65 and finished with a brace of birdies - conceding that he had the best of the weather with the wind having died down - to lead by two strokes from American Bob Tway.
Kenny Hutton, who was the professional at Downfield for 19 years until he left on the ocassion of becoming a Senior earlier this year, had every reason to be pleased with his 71. A surprise winner of the Senior PGA Professional title at Foxhills, in Surrey, in the spring, Hutton was steady throughout in all departments of the game.
Colin Montgomerie, seeking a hat trick of titles after his two victories in the States - the Senior PGA Championship and the US Senior Open - kept himself in the hunt with a one- over 72.
The man who led Europe to Ryder Cup glory in Wales in 2010 described the conditions as "firm and very fast", before adding: "I am hitting 5-irons almost 300 yards out there, which is daft".
But Montgomerie maintained he was under no pressure despite seeking the treble. "I just have to really enjoy myself. If I am brutally honest, I prefer the American style of courses. This is guesswork and I am not very good at guessing," added the Scot, who tied for 21st place at Royal Birkdale last year. He had halves of 35 and 37, finishing with a birdie 4, which could prove crucial in the final analysis.
Paisley-born former European Tour player Ross Drummond, who now lives in Prestwick, was one of the last to finish and closed with a birdie 4 to join Montgomerie on 72.
Edzell's Alastair Webster had halves of 37 and 38 for a 75, a double-bogey 6 on the seventh being his one major hiccup, and former Open and Masters champion Sandy Lyle ended with a five-over 76 following a very mixed round which included triple-bogey 7s on the fourth and 16th and an eagle 3 on the sixth.
Gordon Brand Jr, who won his first European Tour event at Porthcawl -the Coral Classic in 1982 - had a round he will want to forget after crashing to a 13-over-par 84 which included a triple-bogey 6 on the fifth and a quadruple 8 on the 14th. "It was a nightmare," said Brand.