Stephen Dodd, Tony Johnstone, Henrik Nystrom and Pablo Del Olmo finished tied for second at 5-under-par 64.
Johl, who tied for 39th at the 2002 South African Open for his best finish on the European Tour, picked up his first birdie of the day at the par-4 third. He faltered with a bogey at the par-3 fifth but countered with a birdie at the very next hole.
At the par-5 ninth, Johl began a stretch that pushed him to the top of the leaderboard. He eagled the hole and picked up two straight birdies starting at the par-4 10th to move to 5-under.
Johl continued the barrage with back-to-back birdies from the 13th to reach minus-7. Despite a bogey at the 17th, the 33-year-old held on to secure sole possession of first place after the opening round.
Klas Eriksson, James Kingston, Soren Kjeldsen, Thomas Levet, Marten Olander, Dean Robertson, Boonchu Ruangkit, Arjun Singh and Ter-Chang Wang finished tied for sixth at 4-under-par 65.
Ross Bain, Peter Baker, Federico Bisazza, Matthew Blackey, Matthew Cort, Clay Devers, Kenneth Ferrie, Soren Hansen, Barry Lane, Adrian Percey, Rafael Ponce, Gary Rusnak and Simon Wakefield are knotted at 3-under-par 66.
Thomas Bjorn had two birdies and one bogey to finish alongside Nick Faldo in a group at 1-under-par 68.
Jose Maria Olazabal played the back nine first and opened his title defense with a bang. The Spaniard birdied three consecutive holes starting at the par-3 11th to take the early lead.
Olazabal ran into trouble with a pair of bogeys around the turn, however, and his problems continued with back-to-back bogeys from the third. Olazabal salvaged what he could with a birdie at the ninth for a round of even-par 69.
Shih-Kai Lo made a record start on Thursday. The 13-year-old from Taiwan carded a 4-over 73 to become the youngest player to ever compete in a European Tour event. Sergio Garcia, who was 15 when he played in the 1995 Turespana Masters, had been the youngest.
This tournament is co-sanctioned between the European Tour and the Davidoff Tour.
Full-field scores from the Omega Hong Kong Open