The world No 1 signed off with a 74, four-under-par all told, to finish four ahead of South Korea's Jee Young Lee and Swede Maria Hjorth.
"It's hard to describe but it was the most special round I've played," said Ochoa, who has won 12 LPGA titles, including three this year.
"It's unbelievable to win my first major and do it at St Andrews," she said.
"I have so many family and friends here. I wasn't too nervous. I just went out and tried to play my own game and take it hole by hole. But to win at the home of golf is fantastic."
Scotland's Catriona Matthew, among the early pace- setters, closed with 73 for a plus two total, while favourite Annika Sorenstam finished a disappointing four-over.
On the same marks were Becky Brewerton, from Wales, alongside England's Melissa Reid, who claimed the Smyth Salver for the leading amateur.
Ochoa, who took over from Sorenstam at the top of the women's game in May, made three birdies in the first nine holes but was never threatened.
Scare
Her only minor scare was at the par-five 17th where she hit her second into a bunker and had to play out sideways en route to a bogey six.
IT may have been a decade since he last tasted success, but Per-Ulrik Johansson showed he had not lost the knack of winning when he cruised to a six-shot victory in the Russian Open.
Winning from the front is never easy, but the 40-year-old Swede made it look exactly that at Moscow club, Le Meridien, to claim his sixth European Tour victory.
He closed with a 67 for a 23-under-par total to win by six shots from Derksenand seven clear of McLean.
SWEDE Magnus A Carlsson emerged the victor from a magnificent final round battle with Frenchman Michael Lorenzo-Vera at the Challenge of Ireland at Glasson.
Two shots clear at the start of the day, they exchanged blows in a thrilling contest that came down to the very last putt.
HOUGHWOOD assistant Barry Taylor shared top prize with defending champion Aran Wainwright, from Wakefield, with six-under-par 66 in curtain-raising junior pro-am for The Rock, the country's most lucrative region PGA tournament, at Matfen Hall near Hexham.
MANCHESTER'S Andrew Murray finished in a share of 20th place in the Wentworth Seniors Masters, 10 shots adrift of Ireland's Des Smyth.
DANNY Morgan, from Pike Fold, won the Junior League at Swinton Park with 75 as Blackley 15-handicapper Ryan Nevin carded 66 to win the nett.
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