The Scot carded a four-under-par 67 in the DP World Tour event to stay on the coattails of English co-leaders Dale Whitnell, Sam Horsfield and Callum Shinkwin at Rinkven International Golf Club near Antwerp.
Ferguson's compatriot Connor Syme is one shot further back, with fellow Scots Grant Forrest on one under, David Drysdale and Richie Ramsay on level par, Stephen Gallacher three over par and Marc Warren five under par.
Shinkwin claimed a share of the lead in the Soudal Open after almost pulling out of the event with a wrist injury, but it would likely have been a different story if there had been any reserves on site to take his place in the field as the DP World Tour returned to Belgium for the first time since 2019.
"I wasn't really going to be playing today actually," Shinkwin said. "I've had a wrist issue from yesterday (Wednesday) and on the range it just erupted straight up my arm.
"I went into the (tournament) office to see if there was a first reserve around and they said they were in already and had no one else there, so go play if you can and if you can't just walk in.
"Four holes in I was like 'it's not looking good', and then I shot six under. It's nerve damage we think, but nothing a bit of paracetamol can't fix."
Whitnell had an outside chance of shooting the second 59 in DP World Tour history when he covered his first 12 holes in eight under on the par-71 layout, but followed a birdie on the 16th by dropping three shots in the last two holes.
"You can only take the positives really," Whitnell said. "I have struggled the last six weeks or so with a bit of form and swing changes, it has not been quite where I have wanted it to be, but the first 16 holes was flawless.”
Spain's Alvaro Quiros was part of a six-strong group sharing fourth place on five under, while home favourite Thomas Pieters carded an opening 69 which was matched by amateur compatriot Charles Roeland.