Playa del Carmen - Sweden's Robert Karlsson and American Harris English each birdied three of the first seven holes to share the lead when darkness halted the third round of the $6 million PGA OHL Classic.
English matched the low round of his PGA career with a nine-under par 62 in finishing his second round.
Karlsson, an 11-time European Tour winner seeking his first US PGA Tour title, stood on 15-under par with 11 holes remaining in their third round.
The event at Mexico's Mayakoba resort was hit by heavy rain Thursday and the second round did not finish until Saturday afternoon, but organizers expect to complete 72 holes by Sunday night as players will stay in their same third-round threesomes for the final 18 holes as well.
South Africa's Rory Sabbatini and American Kevin Stadler shared third on 12-under, Sabbatini with 10 holes to play and Stadler with 12 remaining.
Spain's Alvaro Quiros and Americans Jason Bohn and Chris Stroud shared fifth on 11-under. Quiros was 6-under for the round with four holes remaining. Stroud was on the ninth hole while Bohn was starting the back nine.
English, who captured his first PGA title earlier this year at Memphis, birdied the par-3 fourth and made back-to-back birdies at the sixth and par-5 seventh holes before sunset stopped third-round play.
"Finally, this tournament my putting has come around," English said. "I went back to my old putter that I played with in college this week, just brought back some good memories and I've really been putting well this week."
Karlsson birdied three holes in a row, the last of them the par-5 fifth, to put himself level for the lead entering Sunday's marathon final charge to the finish.
Stadler, Karlsson and English all stood on 12-under 130 to share the 36-hole lead. But Stadler opened with a double bogey in round three and needed birdies at the par-3 fourth and par-5 fifth to stay three off the pace.
Sabbatini birdied the fifth and seventh as well as the par-3 eighth to stay three behind the co-leaders.
English, who began his second round on the back nine, birdied three of his first four holes, including the par-5 13th. He birdied the par-4 17th and then ran off three birdies in a row, ending the run at the par-3 fourth.
English closed his round Saturday with birdies at the par-3 eighth and par-4 ninth to match the overnight leaders.
Karlsson's two US PGA-best runner-up efforts came in 2010 and 2011 at Memphis. Stadler also has two second-place US tour showings, at 2009 in Greensboro and 2007 at the Reno-Tahoe Open.