Thompson defeated the former World No.1 by four shots, in what was a much-anticipated final pairing at Brickyard Crossing Golf Club, which sits adjacent to Indianapolis Speedway.

With her second victory of the season, the American looks set to leapfrog Sung Hyun Park to become World No.2 in the Rolex Women’s World Golf Rankings.

The 22-year-old begun the week by shooting the round of the tournament – a nine-under 63 – while Ko shot her own 64 the following day, ensuring both the former teen prodigies reached 15-under par prior to the final round of the 54-hole event.

Thompson kisses the track at the Indianapolis Motor Speedway. PHOTO: Andy Lyons/Getty Images.

Thompson played a steady opening nine holes before firing four decisive birdies on the back nine.

“I knew my game was in a good spot,” Thompson said. “I didn’t play my best golf last week in Portland, but I knew if I worked on it on Monday, Tuesday, Wednesday coming into the week, I knew I would have a good chance.”

Meanwhile, Ko found trouble on the 11th hole when her ball settled in a divot that resulted in a double-bogey six – her first, and only, for the week.

The New Zealander signed for an even-par 72 and collected her best result of the year, becoming the fastest player in LPGA history to reach $8 million in earnings (93 starts).

Ko played well tee to green but fell away with the putter in her final round. PHOTO: Andy Lyons/Getty Images.

Ko required 85 putts for the week – compared to Thompson’s 77 – and highlighted that as the main difference between the pair coming down the stretch.

“I just wasn’t putting as well as I did the last few days and that makes a huge difference,” said Ko, who has now gone 28 starts without a victory, the longest winless stretch of her career.

“When you’re in the final round, final group, you kind of want those putts to drop and unfortunately that wasn’t happening for me. Lexi played great, especially down the stretch.”

It has been 10 months since Minjee Lee won her last event on the LPGA Tour. PHOTO: Andy Lyons/Getty Images.

Minjee Lee finished a further shot back in third place, posting her eighth top-10 finish of the year. The West Australian will continue to look to break her winning drought at the Evian Championship next week – the final major of the season.