The American sits atop the leaderboard despite a mixed third round on Saturday.
The Englishman saw a commanding lead cut after a stuttering back nine.
Brooks Koepka made a not-so-subtle dig at Bryson DeChambeau’s “anthill” moment from the first round in Memphis.
The tournament marked the resumption of the tour.
Horsfield fired an eagle and seven birdies in a second round of 63 at the Forest of Arden to share the halfway lead with Sebastian Garcia Rodriguez.
Koepka carded a superb 62 to take a two-stroke lead after the opening day.
A change in date from August to May last year placed the tournament second in line behind the Masters, in calendar terms at least.
The four-time major winner shot 62 in his opening round.
The Northern Irishman needs to win to reclaim the world number one spot from Jon Rahm.