A lengthy delay for rain on Thursday meant half the field had to complete their first rounds on Friday morning, although nobody was able to better Jack Doherty's 69 from the opening day.
But Warren, who had completed a level par 72, then went out and fired a 67 to set the clubhouse target at five under par.
He was joined by Horsey, who was four under par for his round with three holes remaining when bad light forced play to stop for the day, with 45 players needing to return at 9am on Saturday to finish their second rounds.
Felipe Aguilar, Adrian Otaegui and Bradley Dredge share 3rd position one shot behind the leaders although of those leading five players only Warren and Aguilar have completed their rounds.
No Australians or New Zealanders are in this week's field.