Emotional Thompson insists costly breach was 'not intentional'

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An emotional Lexi Thompson insisted her costly rule breach at the ANA Inspiration was "100 per cent not intentional" as she suffered heartbreak at the first major of 2017.

The American, a winner at Mission Hills Country Club in 2014, was hit with a four-shot penalty after being reported by an eagle-eyed television viewer for incorrectly replacing a marked ball in Saturday's third round.

With the sanction not enforced until after the 12th hole of the final round, Thompson's deduction comprised of two strokes for the infringement and another pair for signing an incorrect scorecard.

That wiped out her two-shot advantage and, although the 22-year-old recovered her composure to force a play-off, she lost to Ryu So-yeon after the first extra hole and was left to reflect on a day that sparked much controversy.

"Well it was an emotional day here for me. First off I do want to say what I had done was 100 per cent not intentional at all," Thompson wrote on Instagram. "I didn't realise I had done that.

"I want to say thank you to all the sponsors, volunteers and Mission Hills for making this week possible at the ANA Inspiration.

"Also to the fans out there, words can't describe what you being there for me meant to me. You helped me push through those last holes so thank you for always believing in me.

"A big thanks to my caddy as well for always staying positive and being there for me when it got tough.

"I played some great golf so definitely a lot of positives to take from the week. Time for a very needed three weeks off now. Thank you everybody."

Thompson's woes were compounded by the fact she came up just short with an eagle putt that would have sealed a remarkable victory at the last.