Thunderstorms halted play with much of the field still on the Pula Golf Club course. One of those still out was Richard Finch, who matched McLardy's and Murphy's four-under score but had only played six holes.
Graeme Storm and James Hepworth both posted 67s and are among seven players tied for third.
The first round is to be completed Friday before second-round play begins.
McLardy, who played the back nine first Thursday, opened with 11 straight pars and quickly moved up the leader board with three consecutive birdies. He added another birdie at No. 7 and parred in for a bogey-free round.
Murphy, also starting at No. 10, had a birdie at the 11th hole and then seven consecutive pars. He birdied three of the course's first four holes to move into a share of the lead.