Co-leaders Graeme McDowell and Russell Knox had been enjoying six-under-par final rounds at the OHL Classic at Mayakoba when fading light forced the duo to endure a Monday finish.
The duo both bagged six birdies apiece in what was shaping up to be a thrilling finale for the two Britons, who ended the session on 19-under.
Northern Irishman McDowell finished up on the 13th, with Knox back on 12. The Scot's playing partner Jason Bohn sits third on 17-under, two clear of Scott Brown, who finished on 14.
Overnight leader Derek Fathauer, who has six holes to play, is level with Brown following a disappointing final round so far which saw him finish one-over for the day.
Sweden's Freddie Jacobson is the only European in a four-way tie for sixth as he sits on 13-under, with five holes to play.
