Justin Rose continued his pursuit of the Cadillac Championship with a three-under-par 69 on day three in Miami.
But the Englishman three-putted the last to slip further behind overnight leader Bubba Watson, who shot 67 to extend his lead to three.
Newly-crowned world number one Rory McIlroy is eight shots behind Watson, despite a day's best of 65.
"I'm not sure I can be disappointed with seven under, but if I can today was the day," tweeted McIlroy.
"Could have been a really low one. Plenty of positives though."
Rose started only one behind Watson and looked set to limit his American playing partner to a two-shot lead before his late mistake on the 18th.
The dropped shot means he will tee off alongside Sweden's Peter Hanson in Sunday's penultimate final-round pair, with Keegan Bradley going out last with Watson.
McIlroy, officially the world's best player after winning the Honda Classic, suddenly put himself firmly in contention for a second successive victory with a blistering opening 10 holes.
He went eight under par by rolling home a 17-foot eagle putt at the long 10th, before two late bogeys slowed his progress.
Rose, aiming to return to the world's top six for the first time in four years, remains Europe's best hope of success.
The 31-year-old two-putted the long first for birdie and added another from nine feet at the third.
But Watson had already extended his advantage over his playing partner with an opening eagle and a birdie on the second.
Rose reduced a four-stroke gap to just one with a hat-trick of birdies before the turn, Watson helping him by three-putting at the ninth.
The Englishman caught Watson, who is poised to take over from compatriot Phil Mickleson as the world's leading left-hander, with an eight-foot putt for a fourth successive birdie at the 11th.
But his bogey on the 13th, sandwiched between two Watson birdies, opened up a three-shot gap between the pair, which was maintained by Rose's late slip.
Scotland's Martin Laird, one over par at the start of the day, showed his rivals that low scoring was achievable again by bagging six birdies in his first 10 holes.
Laird finished with a 66 to set the early clubhouse target of five under and rise up the leaderboard.