PLAYA DEL CARMEN, November 16, 2013 (AFP) - Stadler, an American seeking his first US PGA Tour triumph in the $6 million event at Mexico's Mayakoba resort, fired an eight-under par 63 while Karlsson shot 67 to leave both men on 12-under-par totals of 130.
Only 29 of 127 players completed their second rounds after storms pushed the finish of round one into Friday. Some 50 players had yet to tee off. The third round was expected to begin Saturday afternoon.
"It was a very long day, but I couldn't be happier than I am right now with this round," said Stadler, after a birdie at the 18th.
South African Rory Sabbatini and American Chris Stroud shared third on nine-under but were still on the course when sunset came. Sabbatini was at six-under on a bogey-free round with one hole to play. Stroud had three holes yet to finish.
Colombia's Jhonattan Vegas fired a 68 to share fifth in the clubhouse with American Ryan Moore on 134. Americans Pat Perez and Jay McLuen were on the course at eight-under, both will four holes yet to finish.
Stadler has two runner-up finishes on the PGA tour, coming at Greensboro in 2009 and at the 2007 Reno-Tahoe Open.
He birdied the third and the par-five fifth and seventh holes then finished with a flourish with birdies on five of the last seven holes, including back-to-back birdies at 12 and 13 and then again at the last.
Karlsson birdied four holes in a row starting at the fifth and ending at the par-3 eighth, added another at the par-5 13th, but then made bogeys at 16 and 17 before a birdie at the 18th saw him join Stadler at the top.
Karlsson, who has 11 European Tour wins, also has two US PGA runner-up finishes, both at Memphis in the St. Jude Classic, from 2010 and 2011. The Swede only qualified for the Mexico event after a top-10 finish last week on a sponsor's exemption.