The former Manchester United midfielder has needed no time to settle into his new surroundings after moving to PO4 after the expiration of his Luton contract this summer.
The 28-year-old has had a hand in all four league goals the Blues have netted so far this season.
Tunnicliffe fired home the winner in the 1-0 home triumph over Shrewsbury, while he has provided assists for all three of the other League One goals Danny Cowley's men have netted.
The Pompey man is one of six players to feature on the shortlist up for the August player of the month award.
Sheffield Wednesday goalkeeper Bailey Peacock-Farrell, having kept four clean sheets in his side's opening five league matches, is also up for nomination.
Wycombe's Joe Jacobsen, Bolton's Oladapo Afolayan, Sunderland's Ross Stewart and Morecambe's Cole Stockton are the others shortlisted to collect the opening player of the month award this season.
Pompey fans can nominate Tunnicliffe to pick up the award after a blistering start to the campaign.
They don't have long, though, with voting for League One's August winner closing at 9am tomorrow (Wednesday).