The Racing Steps Foundation-backed driver, who made a mistake in the day’s earlier qualifying session, was forced to start from 13th but was confident of his long-run pace to force his way up the grid.
The Arden International racer’s efforts were made far easier at the opening turn, when after making a good start and avoiding the stranded DAMS car of Santino Ferrucci ahead, Dennis made his way up to the inside of the La Source hairpin.
Dennis safely negotiated the turn, but those drivers who opted for the wider exit were caught up in a chaotic incident which ended the race for a number of drivers and proved costly for more.
The incident played into Dennis’s hands though, promoting him all the way up to fourth place into Eau Rouge before a safety car was called to enable the clear up of stranded cars.
Following the restart of lap five, Dennis remained fourth, maintaining a gap of around one second to avoid the dirty air from the third placed car of Trident’s Antonio Fuoco, whilst preserving his tyre life.
With three laps remaining, Dennis made the decision to push and Fuoco’s advantage was immediately slashed, the Italian having no answer as Dennis drove past out of Eau Rouge and rapidly hunted down second placed ART Grand Prix racer Nyck de Vries.
The following lap, Dennis once again made a better exit out of Eau Rouge to pass de Vries, but the time held up behind the Dutchman prevented Dennis from having enough time to catch race leader Charles Leclerc who possessed a five-second advantage.
Dennis’s earlier tyre management enabled him to cut Leclerc’s lead to 2.3 seconds before he ran out of laps as the chequered flag fell.
Dennis will start from seventh place in Sunday’s reversed grid second encounter.
“It worked out nicely up the inside and I started on new tyres as I didn’t run any in practice, so we had the advantage to those ahead,” said Dennis.
“Fuoco ahead was going at decent pace so I kept behind to keep as much life in my tyres. I saw he started to struggle with five laps left and timed it perfectly but just ran out of laps to chase down Leclerc.”