Blackpool boss Simon Grayson believes Pompey’s capture of John Marquis was a statement to their League One rivals.
The striker completed a £1m-plus move to Fratton Park from Doncaster last month.
Marquis is one of the deadliest marksmen in the division, scoring 26 goals in all competitions for Rover last season.
The Blues also brought in the likes of Marcus Harness for a substantial fee from Burton, while experienced defender Paul Downing arrived on a free from Blackburn.
Kenny Jackett’s side are again expected to be challenging at the top end of the division after suffering play-off semi-final heartbreak to Sunderland in May.
Blackpool have enjoyed a fine start to the campaign. They sit second in the table having delivered three wins and two draws in their opening five games.
Grayson is expecting a difficult clash against Pompey and feels it’ll act as a barometer for his side.
The Seasiders boss told the Blackpool Gazette: ‘They’ve got some talented players, with John Marquis up front – the leading scorer in the league last year – being brought in for more than £1m.
‘There are people like Ronan Curtis and experienced players like Paul Downing, so they’ve got a lot of talent.
‘They got to the play-offs last season and that takes some doing, while also winning the EFL Trophy.
‘They’ve got an experienced manager, who knows what it takes to put sides together to get out of this league.
‘But again they will be mindful of what we’re capable of doing. We want to remain unbeaten by 5pm on Saturday.
‘It’s going to be a mark of where we are as a team and we’re there to be shot at because we’re still undefeated. Teams will want to become the first to beat us.
‘Should Portsmouth have gone up last year? It doesn’t matter, it’s history now.
‘It’s about what they’re trying to achieve this season.
‘They’ve sent a signal out to the rest of the division with signings like Marquis, so it’s about what they do this season, rather than what was achieved or not achieved the previous one.’