Leona Maguire laboured to a final day 74 at the Ford Championship in Arizona to finish 19 shots off the lead, where South Korea's Hyo Joo Kim prevailed in a play-off to take victory.
Having bogeyed three of her last five holes on Saturday, the Cavan woman struggled to make any headway in what was her highest round of the tournament.
Her closing 74 saw her slip back to three-under-par and a tie for 68th to take home prize money of $4,653 (€4,300).
Kim beat American Lilia Vu with a birdie on the first extra hole after the pair had finished together on 22-under-par.
Nine birdies in a closing 64 had seen Kim close a four-stroke gap on the American, who had gone into the final round with a two-stroke lead.
Charley Hull, who opened with a first-round 63, had started the day in second but suffered a frustrating afternoon on the greens.
Two bogeys in her opening four holes - both followed by a birdie - were followed by a run of pars before a birdie on the 17th.
She signed for a 71, the only one of the leading dozen who failed to break 70, as she finished tied for 11th, five strokes behind.
