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Matthews, one of four Australians on the books at Pompey, was replaced by Ireland international Conor Shaughnessy midway through the second half, as the home side chased an answer to Mihailo Ivanovic's first half strike for The Lions. 

The away side got in front through Ivanovic in the 40th minute after he lifted a dinked finish over Portsmouth goalkeeper Nicholas Schmid, having been set up by Ra'ees Bangura-Williams.

Bangura-Williams himself will have been disappointed not to open the scoring, having struck an effort wide with an open goal to aim at early on.

Pompey grew into the game after that and could have struck first itself when Josh Murphy slid through to Colby Bishop, but he swung an air shot to miss the chance.

The home side continued to apply pressure in the second half, with Murphy swinging in plenty of dangerous-looking balls, though the forwards could not make a telling connection and Millwall defended resolutely.

On a busy morning for the club's new Australian contingent, ex-Brisbane Roar striker Thomas Waddingham  replaced Matt Ritchie in the 79th minute, keen to replicate the impact he made in his debut against West Brom - where he scored a stunning, albeit consolation, strike in his side's 5-1 loss.

Despite wave after wave of attacks from Portsmouth, Millwall stood up to protect its clean sheet. Bishop could have found an important equaliser in stoppage time, but he could not control the direction of his header under the challenge of Japhet Tanganga.

The victory takes Millwall to 14th in the Championship, 10 points above the relegation zone. Pompey, meanwhile, remain fourth-bottom with a two-point buffer to the drop zone.

Things don't get any easier for Portsmouth, which next faces high-flying Burnley, the Clarets boasting the best defence in the league having conceded just nine goals.