The Irishman took a three week break after finishing in the top 30 at the D+D Real Czech Masters but showed no signs of rust as a bogey free 65 moved him to seven under at Bernardus Golf.
Kearney does not have full playing privileges on the European Tour but has been making his mark on the 2021 Race to Dubai, recording his first two top tens and carding a 61 en route to one of them at the Canary Islands Championship.
He also led the way into the weekend at the BMW International Open and is feeling confident in his surroundings as he battles to earn a card over the closing weeks of the season from 128th in the Race to Dubai Rankings in Partnership with Rolex.
"This year has been positive for me," he said. "I have had a lot of good finishes and put myself in the right spaces and I have grown in confidence from it. I am starting to feel a bit more comfortable which is great."
He added: "I found it really enjoyable, it’s got a real links feel to it. I play links golf at home, so I felt right at home, and I have been at home the past three weeks, so I feel rested somewhat and really enjoyed it.
"I had a chip-in midway through the back nine, that was a bit of help and finished well, a couple under the last three holes so nice to finish that way and holed that one from 30 feet on 18."
Simonsen sent his tee shot a long way left on the 11th but played a brilliant recovery and holed from 28 feet before making another gain on the par five next after hitting the green in two.
He put an approach to four feet at the 14th and then got up and down on the par five last after laying up before holing from 12 feet on the first and hitting the green in two on the fourth for a third gain of the day on a par five.
This year has been positive for me. I am starting to feel a bit more comfortable which is great
He sat alone at the top of the leaderboard but a four way tie was soon established and Kearney and Kieffer were both part of it.
Kieffer left himself a tap-in at the tenth and got up and down from the sand at the 12th but bogeyed the par three 13th after missing the green.
Another excellent approach into the 15th and a 30 footer on the 17th saw him hit back but he found the water on the 18th to turn in 34.
Kearney started on the first and made more serene progress, putting an approach to three feet at the second and holing from around ten feet at the fifth and eighth.
Kieffer then made four birdies in five holes from the third, leaving himself less than 15 feet at the third, fourth, sixth and seventh to share the lead.
Kearney made a five footer on the tenth and chipped in at the 15th before putting an approach to ten feet at the next.
A 25 footer on the last then saw him break out of the pack and lead the way.
Belgian Thomas Detry came home in 30 to sit in the group at five under alongside Canada's Aaron Cockerill, Welshman Rhys Enoch, England's Ben Evans and Sam Horsfield, Dane Marcus Helligkilde, Spaniard Santiago Tarrio and Scot Euan Walker.