World No. 15 Hatton made five birdies and an eagle on the par-five fourth hole to surge ahead of the pack before Harding caught him with a flawless round including six birdies.
Arnaus made his sixth gain of the day on the 18th hole to join the pair at the top of the leaderboard at the European Tour's flagship event at Wentworth Club, Surrey.
"This is a tournament I've been coming to since I was five," Hatton said.
"To lift the trophy here is a goal of mine in my career and hopefully I can play well the next few days and give myself a chance to do that."
Harding was most pleased to keep a clean card on a testing day due to early rain.
"I played good... had good control of my ball flight and my irons. Just a matter of trying to find a few fairways and see if I can give myself a couple of chances on the greens," he added.
"I think everyone teeing it up knows the stature of the event and how important it is for the season."