After carding a 59 playing with friends in Orlando during the coronavirus hiatus, the Englishman signed for a 61 last week in the opening event of the UK Swing to show he still had the appetite to go low.
A 63 on Friday continued that trend and the 23-year-old moved to 18 under after nine holes on Moving Day at Forest of Arden Marriott Hotel & Country Club.
Horsfield started the day in a share of a three shot lead but within three holes he was four shots clear on his own.
He holed from 12 feet on the first and put his approach to tap-in range at the second to move to 15 under.
Playing partner Garcia Rodriguez failed to get up and down for a par on the par five third and with Horsfield making a two putt birdie, the lead was four shots.
A 15 footer on the sixth extended his lead to five shots and Garcia Rodriguez was replaced in second by Korhonen.
The joint overnight leader bogeyed the sixth, while Korhonen holed a long putt on the eighth to complete a hat-trick of gains after a birdie on the fourth.
The two time European Tour winner was soon six back, however, as Horsfield made a two putt birdie on the par five seventh.
Korhonen was joined by Højgaard as last week's runner up made a two putt birdie on the 12th to add to gains on the first, second, fifth and seventh, and another Dane was also impressing.
Joachim B Hansen had eagled the seventh but bogeys on the first and ninth cancelled out birdies on the second and fourth as he turned in 34.
A hat-trick of gains after the turn reignited his round and while he added further birdies on the 15th and 17th, a dropped shot on the last saw him slide to 11 under.
Garcia Rodriguez replaced him in second with an impressive birdie on the tough ninth.