Some eighty runs behind at the start of play with eight wickets remaining, Alex Loudon made eighty but Warwickshire were all out for 272 leaving Lancashire only 68 to win.
Neil Carter had Horton caught by Tim Ambrose for 13 with the score on 29 but that was it and Lancs won by nine wickets in 22 overs.
Lancashire now top the table after Sussex were beaten at Durham. At the other end of the table, Kent knowing a victory would secure their safety had Hampshire following on. They only need four to win in their second innings and wrapped it up in three balls to send Warwickshire to Division Two.
In the Twenty/20 World Cup,Warwickshire's Darren Maddy made only 14 for England against Zimbabwe in Cape Town,South Africa.
England made 188-9 in their twenty overs with Kevin Pietersen scoring 50.
Some good bowling kept Zimbabwe well off reaching the required total. They managed 138-7 to give England a run by fifty runs.
England take on Australia tomorrow at 1pm uk time, knowing that a victory will knock out the Australians.