The Swiss manager, who celebrated his 51st birthday on Saturday, saw his side create a host of chances before the break, but a lack of clinical finishing ultimately cost them.

The visitors thought they had taken the lead after 12 minutes, when Marlon Pack lofted the ball into an empty net. Burnley goalkeeper Gregoire Coudert lay prone following a collision with Pompey’s Ryan Kavuma-McQueen, which referee Ruebyn Ricardo deemed a foul.

After a slow opening, Burnley began to exert greater control midway through the first period. Kyle Walker tested Nicolas Schmid with the first shot on target after 25 minutes, while Andreas Hountondji and Largie Ramazani also drew saves from the Pompey goalkeeper.

Amid Burnley’s long wait for a home league win, which stretches beyond a year, there was evident tension inside Turf Moor.

Marcus Edwards’ inability to fashion a shot after a jinking run into the box drew groans. That turned to stunned silence when Burnley’s No 10 missed from just a few yards, snatching at the ball as it flashed across the box and inexplicably turning it over the crossbar.

The Clarets’ sense of frustration was amplified when Walker was denied a penalty following a trip in the box by Iyad Mohamed, before Ramazani saw a well-taken goal chalked off due to Edwards straying offside in the build-up.

The hosts’ control waned considerably after the break, as the introduction of Ebou Adams and Tyrese Shade for Portsmouth helped rejuvenate the south-coast side. Abu Kamara nearly broke the deadlock on 59 minutes when he cut inside and then arced a shot over.

On Halloween, Burnley’s inability to find an opening goal was a scary reminder of their predicament, with the club still mired in the relegation places.

The biggest cheer of the afternoon came when Josh Cullen was introduced off the bench in the 72nd minute, making his first appearance of an injury-plagued season. But it couldn’t elicit a response from a confidence-shy Burnley.

Ramazani twice failed to connect effectively with crosses to the back post in a game that petered out. The frustration boiled over late on, as Edwards’ erratic performance ended with his withdrawal being jeered by the home supporters.